Kasia's apartment is very spacious and in an excellent location 30 seconds from Las Ramblas and the supermarket. Our host (Kasia's sister Ania in our case) was very friendly and always available to help out. She also kept out of the way and gave us space when we didn't need her which was very professional and appreciated.
This place might be your best option in Barcelona if you're travelling with some friends and want a large, clean, centrally-located flat for hostel prices. I'm very glad we found it!