Lucas and Dawn in the underground of Sinnoh.
The 'Sinnoh Underground' (Japanese: ちかつうろ, Hepburn: Chikatsu Uro, trans. literally meaning; "Underground Passage") is a underground area introduced in the Pokémon Diamond Version, Pokémon Pearl Version and Pokémon Platinum Version. It contains to be a underground area of the Sinnoh region which the player need the Explorer Kit to get entrance to the underground.