Walkthrough
As you complete The Terrible Titans... Lurking Locked Away Adventure, you will have to go through a number of various areas across the Crown Tundra in search of the Regi Legendary Pokemon Group. One of these areas is the Rock Peak Ruins found at the end of the Giant's Bed, which is where one of the Regi Legends can be found. In order to open the door to the ruins, your leading party member must be holding the Everstone. The Regi found within this temple is none other than Regirock, and it can be battled by lighting up the tiles on the ground and clicking on the statue afterwards.
Interactable Pokemon
Regirock: Level 70
We have questions and answers related to this topic which may also help you: