Really thin walls. I was woken up on my second night at 4am to footsteps and lots of noise upstairs. The upstairs unit is also rented out as an Airbnb, and when I met the people, they were reasonable and apologized for the noise- they didn't realize there was someone staying downstairs.
The problem is, even when they did make the effort to be as quiet as possible, when they woke up at 6am the next day, every one of their footsteps could be heard very clearly from the bedroom- since the walls are so thin.
So bring earplugs and a white noise machine if you have any.
Other than sleeping poorly, the place was clean, though a bit dark (some light bulbs were out)- spacious, and a fine place to hang out with my dog for a few days if sleeping isn't an issue.