The flat is located super central in Madrid with walking distance to all the places you would want to see. The street in front of the house is pretty busy, which makes the one bedroom noisy at night.
One of the bathrooms is super small with a tiny shower, which made it difficult for me (1,95m) to shower.
One of the mattresses is pretty used, which makes sleeping in it a little uncomfortable (depends what you're used to).
Exchanging keys and getting extra towel was absolutely no problem, as they have an in-house service.
Communication was excellent.