Neighbor using space behind drywall

Read your condo declaration. It'll say what a unit owner can't mess with.

You could always drill a little hole to see what's back there.

drill baby drill!!!

I believe recessed medicine cabinets are often installed that way, by the original builder.

Get real. Medicine cabinets always use the space between studs.

A friend of ours had this demonstrated to him. His medicine cabinets backs up to his neighbor's microwave. She decided to install a new one and the guy drilled giant bolts right through his cabinet. He went to talk about to her, but she slammed the door on his face. So he just cut the bolts off and patched the holes in his cabinet.

Hope her microwave doesn't fall down now that it's missing it's bolts. Too bad if it does.

Why don't you just move to a pre-war building?

Sometimes people are stuffed inside the drywall. Why do you think it is so cheap?

Don't floorplan dimensions include behind the drywall?