We enjoyed our stay at Apartamentos El Caxigu. The apartment was spacious, clean, and well equipped with basic kitchen supplies -- we were surprised at how much we got for the price! The furniture was comfortable and made for a relaxing stay.
The location is also good. It's within easy walking distance to many of the restaurants within Arenas de Cabrales, and you're a 10 minute drive from the Cares Gorge.
The main things to know:
1) Note the check-in times! This mostly worked well for us, but with a rainy day cutting our activities a bit short, we arrived a little early and there really wasn't anyone there.
2) The parking right by the hotel seems to be fairly limited, as is common with many of the towns in the Picos. Again, we didn't find it to be a major hassle, but it's good to expect it.
3) While the apartment was spacious and comfortable, the construction is not the best quality. In particular, sound travels easily from one unit to the next and we heard noise from children in adjacent units until they finally went to bed. Not a major issue if you're out and about during the day, but if you want a quiet place to say, maybe look elsewhere.
We'd happily book again if we were to be back in Arenas de Cabrales.