The Underground

The Underground (Japanese:  Underground Path) is an area in found beneath the entire Sinnoh region. Players can travel underground at any time using an Explorer Kit, which they can receive from the Underground Man in Eterna City. The Underground features multiple uses of the DS's touch-screen, as the main view is on the lower touch-sensitive screen while the upper screen shows a radar map of the entire underground. It also utilizes DS Wireless Communication to allow multiple players, each with their own DS and copy of the game, to interact.

The Underground has a different menu from the one in the overworld. Mostly, it shows the different items used; with the exception of treasures, which can be transferred to the player's Bag, these are all exclusive to the area.

Spheres are the currency of the underground. The player can bury their spheres to make them more valuable, either by leaving a sphere buried for a long time to make it grow, or by burying spheres of the same color in the same spot to merge them into a larger sphere. When spheres are buried in the same spot, their sizes are mixed together. When two or more spheres are buried on top of each other, the largest sphere is added to the smaller spheres' sizes divided by five, rounded down, plus one. Spheres can reach a maximum size of 99, with some growing faster than others. Blue, green, and red spheres grow the fastest, and are thus the least valuable. Pale spheres are the second fastest growing spheres, and are semi-valuable. Prism spheres are the slowest growing spheres, and are thereby the most valuable of all the sphere types. Burying spheres can increase the number and density of mining sparkles in the same vicinity.

There are six different areas in the Underground; each is accessible from different overworld locations. While some are readily accessible from the mainland, players must sometimes travel to far-off places like Fullmoon Island to enter these areas.

Exploring
As in the regular world, using the D-pad lets the player walk in any direction and holding "B" allows running. As the regular Bag is not able to be used in the Underground, the Bike is not available to increase speed further. Steps taken in the Underground do not count towards hatching s or the Counter App, but time spent counts towards the overall game timer. The game cannot be paused (by closing the DS lid or otherwise) while in the Underground. Additionally, since the wireless features consume more power than usual operation, the player should be careful not to drain the battery completely while in the Underground.

There are six independent sections of the labyrinth, each accessible from different places in Sinnoh. In terms of vendors and mining treasures, the areas are equivalent. When participating in multiplayer action in the Underground, players should make sure they are all in the same set of caverns.

The vast majority of the tunnels are 5 squares wide, with some single-square-width passageways between parallel tunnels. The player can see roughly 12x15 squares on the screen at any given time (not accounting for side effects of the top-down perspective). By touching any area of the lower touch screen, a radar pulse indicates interactive objects within a 4-5 square radius, indicated by yellow sparkles. There appears to be a maximum of 8-10 sparkles that will display if a particular ping returns too many objects.

If a sparkle revealed by a ping is located on the floor of the tunnel, it is either a trap or a sphere. A difference in whether a sphere or trap is hidden in the sparkle, a trap has a white sparkle while a sphere has a golden one. If both are hidden in one spot, a trap is found first, then a sphere. If the sparkle is in the wall, it is a bulging section that can be mined.

Mining
One of the main attractions of the Underground is the mining minigame. To mine, the player must find a spot where the wall 'pings' by touching the screen and looking for sparkles. These spots will appear randomly in the Underground, usually in clusters, and can be located by looking for sparkles marked on the radar screen. They appear more frequently near buried spheres, and so one way players can ensure they always have a lot of mining spots available to them is to make a "sphere garden" by burying many spheres in the same area.

The game itself is similar to or. At the start, the cave wall is shown, represented by a grid full of squares. There are three depths of wall: the tan soil, which can be broken through in one hit, the darker soil, which needs two hits to be broken through, and the large rocks, which each need three hits to be broken through. The player digs into the wall with a pick, which chips away small areas of rock, and a hammer, which breaks a larger area of the rock. Each spot will hide one to four items, including spheres, Fossils, Revives, Heart Scales, shards, pre-Generation IV evolutionary stones, Plates, and a few held items. Iron pieces are also in the wall, which cannot be dug out and prevent further mining upon discovery (that is, when they are uncovered on a direct hit, no other spaces are revealed until the next hit). Upon hitting a piece of iron a small 'ping' will be heard. Each hit will bring the wall closer to collapsing; if the wall collapses before everything is dug up, the game ends and the player is rewarded with what they dug up before the wall collapsed. Spheres the player has mined are stored separately from other items (called treasures in game); up to 40 sets of spheres and up to 40 treasures can be carried by the player, in order to acquire more, he or she has to make room in the Underground's Bag, for example, by burying the spheres or by sending the treasures to the Bag in the overworld.

In addition, if anyone else is mining nearby, a pickaxe will appear on the player's screen wherever the other player hits on their screen. This helps clear the wall without contributing to the wall's collapse.

At first, only Skull Fossils or Armor Fossils can be found depending on the game version or the last digit of the player's Trainer ID number. After obtaining the National Pokédex, however, the game will also yield Helix Fossils, Dome Fossils, Old Ambers, Root Fossils, and Claw Fossils. A number of items that were found rarely prior to obtaining the National Pokédex can also be found more easily now, such as the evolutionary stones. Furthermore, in the games, Fire Stones, Thunderstones, Sun Stones, Heat Rocks, Icy Rocks, Helix Fossils, and Claw Fossils can be found more easily in Diamond, while Water Stones, Leaf Stones, Moon Stones, Damp Rocks, Smooth Rocks, Dome Fossils, and Root Fossils can be found more easily in Pearl. Like the Skull and Armor Fossils, Platinum uses the Trainer ID to determine which set of treasures is more common.

Burying spheres
Burying spheres is done through the Underground's menu function. It will not work, however, when the player faces a wall: spheres can only be buried in the ground. The longer the spheres remain buried, the larger they will grow. In the player's presence, their buried sphere will occasionally let off a bright glint. Buried spheres are only accessible to the player that put them there; others cannot see them, ping them, or interact with them in any way. Others can, however, take advantage of the increased mining spots generated. This can be beneficial for the player who buried the spheres and a friend (or friends), as there will be plenty of opportunities to mine side-by-side.

Item shapes
Items have unique shapes in the mining minigame. Larger items cover a greater area and can thus be found more easily, but take more digging to unearth.

{| align="center" style="font-size:85%"
 * colspan="5" | * Can be found this way and rotated 90° ** Can be found this way, rotated 90°, rotated 180°, and rotated 270°
 * - align="center" style="vertical-align:bottom" |
 * width="20%" |
 * width="20%" |

Small Sphere


 * width="20%" |

Large Sphere


 * width="20%" |

Heart Scale


 * width="20%" |

Skull Fossil


 * width="20%" |

Armor Fossil


 * - align="center" style="vertical-align:bottom;" |

Dome Fossil



Helix Fossil**



Old Amber*



Claw Fossil**



Root Fossil**


 * - align="center" style="vertical-align:bottom;" |

Red Shard



Yellow Shard



Green Shard



Blue Shard



Plate


 * - align="center" style="vertical-align:bottom;" |

Hard Stone



Heat Rock



Damp Rock



Smooth Rock



Icy Rock


 * - align="center" style="vertical-align:bottom;" |

Fire Stone



Water Stone



Thunderstone



Leaf Stone*



Moon Stone*


 * - align="center" style="vertical-align:bottom;" |

Sun Stone



Oval Stone



Everstone



Iron Ball



Light Clay


 * - align="center" style="vertical-align:bottom;" |

Odd Keystone



Revive



Max Revive



Star Piece



Rare Bone*


 * }

Secret Bases
The Underground is also where Secret Bases are created in the Generation IV games. The spheres dug up in the mining minigame can be traded to explorers found throughout the caves for objects to furnish Secret Bases. Secret Bases can be created in any part of the wall using a Digger Drill. These bases can be decorated with ten items each.

If a player visits a Secret Base of another player, they can get that player's flag. After successfully returning the other player's flag to one's own base, the player's record is updated. The number of flags captured (either from the same "opponent" or several ones) upgrades the player's Secret Base computer. Each upgrade changes the graphic slightly (the icons resemble the evolution of personal computer technology) and also allows the player to remove additional boulders from their base using the "Store" option of the "Decorate" menu. This allows more room for decorations to be placed. Boulders that have been removed cannot be placed back into the base, although they'll reappear if a new base is created. By default, player can use only 10 decorations.

A player who has a flag cannot do anything besides store the flag in their PC. If they try, the game will alert them that they have to drop their flag first. If the owner of the flag talks to someone who has stolen it, the flag is automatically returned to their base, while if another player talks to someone who has stolen a flag, that person steals the flag from the other person, and then they can try to get the flag to their base.

Traps
Another feature of the underground is traps. These can also be purchased from explorers with spheres or found in the path in the same manner that the player can find mining spots: by touching the screen and watching for sparkles on the ground. They may also be dug up, like the Spheres, by pressing the A button when next to one, facing it. Players may only carry a total of 40 traps at one time; an attempt to unearth a 41st trap will be refused and the trap left where it is. If a player steps on a trap, they may be sent flying in a specific direction, have their controls altered so they walk the wrong way, or they may have to use the stylus or microphone to clear a hazard, such as by popping bubbles or clearing smoke, or a message will be broadcast to all players in the Underground. The game will explain how to escape from a trap, however if the trap was placed by an opponent, he or she will be alerted that someone has landed in it. If one player is caught in a trap, another can face them and press A to immediately get them out of it. Since all players run at the same speed, well placed traps are the primary means of catching up to someone who has stolen a player's flag. If a player has set some of his/her own traps they will show up as brightly colored squares with symbols matching their names. This helps the player as to not get caught in her/his own traps.

Vendors
A crucial feature of the underground is vendors. These explorers appear to be stationary and only rotate in place. There are three types of vendors in the underground. The first group of vendors are those who accept the player's treasures and give them spheres in return. The second group of vendors are those who accept spheres and give goods in return, and vice versa. The last group of vendors are those who accept spheres and give traps in return, and vice versa. Vendors change their prices on items and which items they sell every day, so one vendor may not have the same item for two days in a row. Vendors allow the player to decorate their Secret Base and plant traps anywhere in the underground. In the map of the underground at the top of the page, the yellow dots are the trap vendors, the red dots are the treasure vendors, and the blue dots are the goods vendors.

Getting to areas
Top right area: Fight, Survival, Resort Areas

Top left area: Fullmoon Island, Newmoon Island

Bottom right area: South Sunyshore City

Bottom left area: Twinleaf Town, Sandgem Town, Jubilife City, Oreburgh City, Floaroma Town, Canalave City, Route 221, Pal Park

Small center area: Celestic Town

Multiplayer
When entering the Underground, the DS Wireless Communication is activated. Other players within range choosing to enter the Underground will be able to interact in the same set of tunnels. As described above, players can enter one another's Secret Bases and set traps. Additionally, digging in the walls next to each other allows players to collaborate on the excavation.

Players can talk to each other just like NPCs in the above world. In doing so, they can exchange Goods used to decorate a Secret Base, and they can communicate using a basic question and answer selection menu. Each time a player talks to another player, the counter on their card is incremented. This counter reaching 32 is one of the prerequisites for encountering.

Item appearances
There's a 20% chance for an item to be found in a bulging wall. Some items, such as most of the fossils, can only be found after obtaining the National Pokédex.

In the anime
The Underground appeared in The Grass Menagerie!. While was battling Gardenia for the,  stumbled across the sprawling tunnels of the Underground. They met the Underground Man, who convinced them to dig in the tunnels for Shards and Spheres. They agreed to split the profits with him in exchange for lunch. However, he fled with the treasure while they ate.

In the Pokémon Adventures manga
The Underground's network of tunnels enabled Professor Rowan, Mr. Berlitz, the Underground Man, and the Gym Leaders of Sinnoh to reach the Spear Pillar and assemble without Team Galactic noticing near the end of the.

Trivia

 * Air vents that serve to provide the Underground with a supply of air can be found all over the surface of Sinnoh.
 * Walking into a wall will not cause the 'bump' audio to play.
 * The Underground has rotational symmetry.
 * The player's PC is only updated when the door is shut; if it is open then the PC reverts to the very first look.
 * The Underground is featured in one of the paintings on display in Lumiose Museum in Pokémon X and Y.
 * The Underground's background music is partially a remastered theme.

In other languages
Untergrund (Sinnoh) Subsuelo Souterrain de Sinnoh Sotterranei ちかつうろ 地下通道（神奧）