Swamp hut

Swamp huts are generated structures that have the ability to spawn witches and (upon generation) one black cat.

Generation
Swamp huts generate rarely in swamp biomes. However, they do not generate in the swamp hills biome variant.

Structure
Swamp huts consist of a small square "hut" made of spruce planks, with oak log "pillars" extending down to the ground. There is a small platform outside of the hut that could be an entrance; however, it is many blocks above the ground, and there are no stairs that go upwards to the hut. The roof of the swamp hut is made up of spruce wood stairs and spruce wood planks.

The inside of a swamp hut consists of an empty cauldron, a crafting table, and a flower pot with a red mushroom in it.

However, in Bedrock Edition, the cauldron generates with a random potion inside of it in random amounts. These potions include Swiftness, Slowness, Weakness, Healing, and Poison. Water Breathing, Fire Resistance, Night Vision, Harming and Decay seem to have a very low chance of being spawned, also rarely the cauldron contains a splash potion. This is the only way to legitimately obtain Potions of Decay, since the potion cannot be brewed.

Mobs
Upon world generation, one witch and one stray black cat spawn inside the hut. These never naturally despawn, however, the witch will not spawn when the difficulty is set to Peaceful.
 * (one spawns in the hut)
 * (one spawns in the hut)

Additionally, in the 7×9×7 area that is the hut (this is the size of the roof and one block over the porch, from one level below the floor of the hut to two blocks above the roof) only witches can spawn, while all spawned cats (from spawn eggs, breeding and commands without cat type set) will always be black.

Trivia

 * The "hut" part of a swamp hut generates on or above the surface, while the wood "pillars" extend down until they reach solid ground. This means that if part of a witch hut is at sea level and another part is on top of deep ground, such as a ravine, the pillars on the deep-ground side go all the way down to the ground.
 * It is possible for swamp huts to generate on top of one another.
 * Swamp huts are one of three generated structures that do not have a loot chest (the others are fossil and desert well).
 * Swamp huts are the only generated structure that is designed to stand on top of a water surface (due to their appearance).