Casa Cosi is a nice, clean, modern, cozy (and small) apartment in the heart of Barcelona. Our host Sylvia was an excellent communicator, as was Neil, the person she appointed to meet us with the key. It's a 9-minute walk from the Hospital Metro station, so if you have a lot of luggage, take a taxi (Barcelona has sided with them instead of Uber, unlike practically every other place in the world).
There are a couple of caveats if you are sensitive to light or noise. The Holy Trinity of sleep science is "cool, dark, and quiet." Casa Cosi delivers wonderfully on cool with powerful air conditioning in both bedrooms, kitchen and living room. A unique feature is the lack of exterior windows, which feels a little weird, but is fine. So to say that the apartment "overlooks an interior patio" isn't entirely accurate. The windows are all on the ceiling in the kitchen, which lets light stream in in the morning, not just to one room, but all of them, because every room in the apartment has interior windows near the ceiling. I recommend bringing an eye shield or black T-shirt to put over your eyes if you want to sleep in.
The interior patio is in fact some sort of restaurant, and an open grate in the kitchen lets every sound in. The result is that until at least midnight on the Satuday we arrived, we heard dishes clanging and people talking and laughing as if they were in the apartment with us.
The bottom line is that Casa Cosi can be an excellent place to stay, as long as you're OK with a couple of its unique elements.