Our family (3 persons) visited Barcelona for a week. Piias & Fernandos apartment is very nice, clean and has all what you need (air condition an wifi included).
Although the location of this flat is really centric (what a luck) it's really quiet and you will have no problems to sleep in the night.
Piia is a wounderful host, helpful and very friendly. We absolutely recommend to book Piias & Fernandos apartment.

P.S. If you have heavy luggage: There's an elevator ;)