Our family of four, two adults, two children, stayed in this apartment. It is in a lovely old building in Barrio Alto, but the area is quiet. We did enjoy staying here, but the mattress on the main bed is really, really uncomfortable. The sofa bed, where the children slept, is also quite dirty - again a new mattress would be beneficial.
The views from the balcony are lovely and the air con is great. The area is lovely with main nice bars and restaurants not too far away.
Please note, that whilst the kitchen has plates, cups, etc, you are advised to leave everything clean - but there are no dishwasher tabs, detergent, cloths, etc to do this.
Overall, I would stay in the apartment again, but a few upgrades by the owner (new mattresses and items in the kitchen) would make it perfect.