The idea here being some kind of abandoned rotting mansion that spawns in the Marsh biome. Think of it as the Betweenlands equivalent of the woodland mansion
The building would be comprised of four levels. An attic, a second floor, a ground floor, and a basement. The interior is poorly lit, the only part that is "well lit" being the foyer. the wooden floors and roof have gaping holes. The Basement being flooded with waist deep (1 block deep). Due to the instability of the marsh ground, The mansion also has a fissure that nearly splits the building in two. The smaller detached half being far more deteriorated than the rest of the mansion and being a block lower in the ground due to that half sinking into the ground.
this is merely a basic premise. I'd like to see what WightofShadows would think of this concept.