Diglett's Cave/Differences between generations

In Generation II the cave was slightly shorter than in Generation I, and the southern entrance was also in Vermilion City, instead of like every other generation.

In Generation III the cave was much longer than in any other generation.

In Generation IV the cave is the same length as it was in Generation II. This makes it one of very few Kanto areas to retain its length from Generation II. The only change is the addition of walls, that allow access to a higher level of the cave.