Professor Snape's Office
Snape is in the habit of keeping the place dimly lit, judging from Harry's visits during his second (CS5), third (PA14), fifth (OP24 and other tutorials), and sixth years. Snape has a fireplace (which is sometimes lit) that is apparently connected to the local Hogwarts Floo network, since he was able to call Lupin (then working at Hogwarts) through the fire, and Lupin was able to travel through the fire to Snape's office.
The walls, which are in shadow, are lined with glass jars, including the wall behind Snape's desk. Each jar contains some potion (differently coloured in different jars) in which is suspended slimy bits of some animal or plant (different ones in different jars). For example, one jar contains a large dead frog suspended in some purple liquid (OP26). Snape also keeps a cupboard in one corner containing his private stores of potion ingredients. Snape also keeps a wall clock, occasionally an extra table, and a chair or two for visitors (HBP24).