From Bulbapedia, the community-driven Pokémon encyclopedia.
Hippowdon Temple (Japanese: カバルドンしんでん Kabaldon Temple) is a location in Pokémon Ranger: Shadows of Almia. Oddly enough, despite its shape and name, no Hippowdon live inside, though there is one of them just outside.
The temple is rigged with many traps, such as Bronzor hiding in the walls, disappearing floors, arrow panels that push the player in various directions, and cannons that launch balls of sand, which can cause damage to the Capture Styler and knock the player off the path that must be followed. A Cresselia appears as the guardian of the Yellow Gem in the final room. This Pokémon cannot be caught anywhere else, excluding the Capture Arena, and cannot be kept. A Starly can be found (if it is not already the player's Partner) in the temple on a quest. Once caught, Starly will join the Partner Farm, as will Hippopotas. After completing the game, a Dusknoir will appear with all the Claydol. Palkia can be found here on a special mission. Once caught, it cannot be kept. It cannot be caught anywhere else.
Upon completing all 60 Quests and completing the Browser, a whirlpool of sand appears in a room deep in the temple, that before was a damage ground, in the room with the arrow panels. If the player enters this whirlpool, they will be dragged to a hidden room containing the inscription "The final Pokémon that should be etched in the memory of the chosen one...the final Pokémon lies asleep inside" and three pedestals. If Regirock, Regice and Registeel are brought to this room and placed on the pedestals, the player may enter a battle with Regigigas. After the first capture, the player may return at any time to challenge Regigigas again, not needing the legendary golems. Regigigas cannot be kept, and this is the only place that it is found.