The Assassin Brotherhood's base in Assassin's Creed Revelations is the Galata Den.
The Galata Den is located in Constantinople, the main city explored by Ezio Auditore in Revelations. Ezio uses the den as a headquarters while searching for Altaïr Ibn-La'Ahad's legacy and the keys connected to the Masyaf vault.
The game divides Constantinople into districts and introduces a system in which Assassin dens can be threatened by Templar control. Defending and managing these locations forms part of the broader city-conquest mechanics, while the Galata Den remains the central base associated with Ezio's activities.
Ravensthorpe belongs to Eivor in Assassin's Creed Valhalla, and Villa Auditore is Ezio's family home and headquarters in Assassin's Creed II. “The Hideout” is a generic phrase used for bases in several games, but it is not the specific name requested here. Revelations was released in 2011.