The Endermaster's Castle is a castle in the End that appears in Willcraft's Endventures series introduced by the Ender Triplets. It is first 'whole' appearance was found in Endventures Episode 6 - Shadow's Identity Crisis. While the throne and some of its interior introduced in the first episode.
The Endermaster's Castle also has a download available by Willcraft, although this is the 2013 version.
As above, the castle is on the main island in the End. It sports extremely high walls with an even higher tower at each end of a row of walls, creating a box-shape. Above the significant front gate is a large obsidian sphere connected to two of the towers. It is a medium sized room with a unique pattern on the floor, and was used by The Endermaster for a ritual later in the series. The walls and towers are composed of obsidian, and the front gate is guarded by a drawbridge made out of bedrock, a moat of lava that surrounds the entire castle, a gate of iron bars behind the drawbridge, and oak-wood doors as the final barrier. The drawbridge and gate are controlled by a large lever on the castle's rooftop, guarded by an Enderman. The features just mentioned have been removed as of the latest revision of the castle however.
The interior of the castle past the gate doesn't feature a lot of decor. Inside the castle is a floor made of regular stone bricks. There isn't any objects nor blocks inside that produces light, and there are a few minor decorations such as small obsidian pillars. Also, on the side walls are 3-block tall doorways most likely connected to the top of the walls for the guards. There is a throne 4 times the size of the Endermaster, but due to his shape-shifting ability, he was able to adapt to its large size. There is most likely an army of Endermen that guards the castle in the case of an attack.
It is controlled by the Endermaster, so he would not have to live in the void, who uses it as a base of operations, a home, and a meeting room where he can see his minion Endermen. The Endermaster would mainly sit on the throne to direct and give orders, but later in the series, he would set up a ritual in one of the upper towers with a Dragon Egg, in order to revive Enderia after she was killed by The Wither King. Wrecker and Shadow would also later fight on top of the castle during the battle between The End and The Nether.