The Grand Underground in Pokémon Brilliant Diamond and Shining Pearl is a vast network of tunnels and biome-based caverns, named Hideaways, in which you can find numerous Pokémon.
Divided into six separate areas accessed from different parts of the overworld, we've put together a guide to what Hideaways you can access, and what Pokémon you'll find in them.
To help you get your bearings, here is the complete map of the Grand Underground and the different Hideaways.
Here's how you can get started in the Grand Underground.
Each Hideaway has a different biome type, allowing you to catch different Pokémon. For example, a Fountainspring Cave allows you to catch Water and Grass-type Pokémon, while you'll find exclusively Fire-type Pokémon in a Volcanic Cave.
Note that leaving the Hideaway and reentering will change the Pokémon found inside. This is useful if you're looking for a specific Pokémon, because you can just keep exiting and entering until the one you want appears.
The levels of Pokémon you encounter in the Grand Underground depends on how many Gym Badges you have, so if you're looking for the strongest, wait until you've beaten the Pokémon League.
Note: To start with, you'll only find Sinnoh Pokémon in Hideaways. Unlock the National Dex to spawn more varied Pokémon.
Here are the different biomes you'll find in Hideaways in the Grand Underground. Use the Find function with Ctrl+F (on Windows) to find specific Hideaways or Pokémon.
Pokémon specific to one version will be listed in (brackets).
Images and source data: Serebii.net / game8.
