Overall, I highly recommend Carmela's place in Madrid. The terrace is so lovely, perfect for watching the sunset with a glass of wine. Sleeping in the attic is super fun, and the apartment is easily spacious enough for 4 people.
The location is great, right by the Sol station and walkable to most sights in Madrid.
The only gotcha is that the bathroom doesn't lock, but you can easily figure out a code for that amongst your friends.