GLaDOS Chamber

History
The chamber was built and used for housing GLaDOS, presumably out of a renovated enrichment sphere. As Cave Johnson would say, "All joking aside, those asbestos particles would most likely act as a magnifying glass for those neurotoxin generators we put in that room. Hey, wait a second! Why am I alive to be saying this! I died of moon rock poisoning last...(Recording cuts out).

Appearances
The original chamber appeared at both the end of Portal and shortly after the beginning of Portal 2. The portal 2 version is much messier and more destroyed looking, yet includes even the littlest details of the Portal version. Only two of which being the small office area that you enter through before you fight GLaDOS in Portal, and a catwalk (that is now collapsed).

The new chamber
When the chamber appears later in Portal 2, it looks completely different without an incinerator shaft, and several small circular panels, one in each corner. It is unknown wether GLaDOS did these renovations to keep it from collapsing, or if the original chamber DID collapse and GLaDOS rebuilt it completely.

Wheatly Chamber
The chamber also has an alternate appearance when being used by Wheatly. This appearance is the same as the "New chamber", but with a high catwalk and the stalemate resolution annex has no stairs leading up to it.