The Lich Tower is a landmark from the Twilight Forest mod. At the very top of this tower the Twilight Lich lives, rules, and performs sorcery. The Lich Tower has a large main room, and a bunch of smaller rooms stemming off of it. Zombies, Skeletons, Death Tomes, and Swarm Spiders can be found here, usually with a Mob Spawner block. The Lich Tower can have many different types of treasure, though usually just Books, brewing supplies, potions, and enchanted equipment.
There is no main entrance, so you must break your way into the tower to gain access, which can only be done after killing the Naga, as breaking any parts of the tower before-hand will not allow you inside, as the blocks will regenerate the instant you break them.