What is a locked den in AC revelations?

In "Assassin's Creed: Revelations," a locked den refers to a specific location within the game that is part of the Assassin's Brotherhood's territory. These dens can be fortified and are critical for the player to control as they provide resources and strategic advantages. To access a locked den, players must complete certain missions or objectives, often involving defeating Templar forces or overcoming obstacles. Once unlocked, they can be used as safe havens and bases for further operations within the game.