The Slime Farm is a large, undecorated room with torches filled all over the stone ground of the room. The walls and other surfaces are "stained" with remnants of ores that were mined or cobblestone that served as fillings for empty spaces. The entrance has a little pool of water so you can jump down from the top safely and a ladder if you want to leave the Slime Farm. There is also Porky's grave beside the entrance, as well as a painting.
The Slime Farm is used to spawn large slimes for harvesting slime balls. Other googlies also frequent the part of the house.
Stampy built (or perhaps dug out) the Slime Farm in one of his early episodes. In one particular episode, Porky passed away after falling from the top of the ladder, and missing the pit of water below. His grave is in the Slime Farm for this reason.