We loved our stay in Sergio's apartment - firstly Sergio was so so helpful from start to finish - we asked a million questions and had various requests as we went and he couldn't have been more helpful or supportive. The apartment's location is wonderful too - a 2 minute walk from a metro station and a 5 minute walk from Las Ramblas de Poble Nou which is an amazing mile or so of restaurants and cafes and shops. The beach is just a 10 minute walk and in 2/3 metro stops you are in the centre/old town.
The design of the apartment is great, and it is really light and bright and peaceful. We'd thoroughly recommend and also on the door step is an amazing restaurant called KOH - it is Asian but incredible and a welcome break from all the tapas consumed on the Ramblas from time to time!