The Dungeon Towers are structures located around the End dimension, relatively far from the Dragon Lair.
Each of the structures consists of two parts: the floating island, and the tower itself. The basic shape of the island is a cone, with a large amount of random inconsistencies to create a feel of crumbling island. The tower lies in the center on top of the island and consists of 3 basic rooms and 1 chest room, with the Ender Eye mini-boss lying on the very top of the tower.
Each tower has 4 floors inside - 3 regular floors and 1 chest floor. There are 9 regular floors to choose from, 3 chest rooms, and there can be multiple same rooms which means there are 2187 different ways for the floors to generate.
Each room has a base layout with special variations (flower pots may rarely have dead Death Flowers, a brewing stand has a 1 in 100 chance to be Enhanced Brewing Stand) and some may also have lootable blocks (dispensers, furnaces, chests, brewing stands) with a variety of items.
Most of the floors (including chest floors) have Angry Enderman spawners, which have one or more of the following potion effects: strength, invisibility, swiftness, regeneration, resistance and fire resistance. The amount of effects and their levels depends on the floor - the higher you go, the worse effects they will have. The spawners also spawn less amount of mobs than a vanilla spawner would, but they do it quicker.
Both the Angry Endermen spawners and the Ender Eye miniboss are a challenge to overcome and it is definitely suggested to bring similar gear you would for the Hardcore Ender Dragon battle - enchanted diamond armor and sword, potions etc. It is also suggested to bring Ender Pearls, Spatial Dash Gem or Transference Gem in case you happen to be pushed off the tower.