underground (sinnoh)
The Underground is a large area comprised of many corridors located underneath the whole region of Sinnoh, accessible in Pokémon Diamond, Pearl and Platinum.
Multiple players can interact in the Underground via the DS Wireless Communication.
Some activities available in the Undergound include:
- Digging items such as fossils and evolutionary stones from the walls.
- Building and decorating a Secret Base.
- Finding the Secret Bases of other players and capturing their flags.
- Placing traps on the ground, which often negatively affect the movements of players who step on them.
See Danbooru post #3364990 for a piece of official art depicting the Underground.