The Rock Peak Ruins (Japanese: いわやまのいせき Rock Mountain Ruins) is a special cave in the middle of Route 228. It is only accessible in Pokémon Platinum, when the player has an event Regigigas in their party. It is called the Rock Peak Ruins because it is the home of Regirock, the Rock Peak Pokémon.
If the player enters the cave without the event Regigigas, the cave is simply part of Route 228.
A "statue" of Regirock is present. By stepping on the 7-dot pattern on the floor and walking up to the statue, Regirock will attack. It is at level 30. It can be rebattled multiple times as long as the Event Regigigas is in the party; however, it can only be caught once.