I definitely recommend this apartment, nice, clean and with two terraces! which are awesome to take some rest at the end of the day. Monica is a very friendly host and we had zero problems during our stay. It's on the top floor, but there is an air conditioning so it's not a big issue even in sunny days.

The building is in quite a decent location - close to the metro station from which you have approximately 15-20 mins to the center (Barri Gòtic etc.). At the bottom of the building you have a nice and cheap baker/cake shop (coffe costs ~ 1 euro). Three big supermarkets are one metro station from Collblanc (Badal) - a 10 minutes walk, make sure to buy some Cava there ;-).

Don't be affraid of the metro. Buy a T10 card, 10 trips will cost you 10 euro, one card may be used by two people. You can switch the lines using a single ticket, up to 75 minutes. Most of the time you'll travel twice during the day: to the place where you start sightseeing and back. Most of the interesting things to see can be located in a walking distance if you plan things properly.

If you like motorsport, check the schedule of events @ Circuit de Barcelona-Catalunya, you can get there by train, if you're lucky you may see some race and get into the pits to take some cool pictures, everything for free!