The Isle of Solitude, also called GM Island, located in the way between Carlin and Greenshore is inhabited by CIP members and Gamemasters before they were excluded from the game. The building on the island has four floors:
- basement with prison cells
- ground floor has a Big Table and Chairs
- first floor has Bookcases and a balcony
- second floor has some furniture and a Portal of Citizenship for the island.
This island is only accessible to CIP members who can legally teleport there. The existence of this island has been debated, and many envision criminals brought here to receive their punishment.
As we can notice in Guido's (and a lot of Cip members) character page, their residence is "Isle of Solitude".
Source: https://tibia.fandom.com/wiki/Isle_of_Solitude