Thanks to tech M happened to have on him when ported in, he was able to re-grow (comics!) a pretty much exact replica of his apartment that exists between cities here. The only way to gain access is through a glowing golden-orange Door that only M can create.

This is what it looks like:



And the text I pretty much use whenever I need to describe the apartment is:

M's apartment is a large, modern two floor loft with neutral walls, ceilings, and floors, though it's most striking feature is that it has no windows and doors. The first floor, is an open space with a few columns for support, with the space divided into several areas: the small kitchen area is to the far right, with a large island separating it from the rest of the area, the living room, is closer to the center of the room on the left, with a pleather sofa, sectional, and armchair set up in a u-shape around a sparse entertainment center. In the far end of the room on the left left is a large table for eating or planning, and to the right is a billiards table beneath the floating stairs leading to the second floor.
The second floor is pretty sparse, consisting of some gym equipment in one area, and a dresser and an armoire in another. He doesn't like to sleep in a bed, so he doesn't have one.