From Bulbapedia, the community-driven Pokémon encyclopedia.
Rasp Cavern (Japanese: ヤスリどうくつ Yasuri Cave) is a location in Pokémon Ranger: Guardian Signs.
It is located north west of Teakwood Forest on Renbow Island. At the back of Rasp Cavern is a door that leads to a trial room which is blocked off until the festival, wherein the player obtains the Rainbow Grail after completing several challenges, including one very similar to the Sootopolis Gym. There is a Drapion lithograph covering up a chamber in the cave. The player can break the lithograph and gain access to the chamber by clearing the first Forest Temple past mission.
In the anime
Rasp Cavern appears in the special episode Pokémon Ranger: Guardian Signs (Part Two). In the special, Ben and Ukulele Pichu travel to the cavern to confront the Pokémon Pinchers. They try and fail to prevent the Pinchers from stealing the Ranger Sign on the tablet and Ben fights a Cranidos controlled by the Pinchers.