The main thing to know is that the location is fantastic. Right in the heart of Barrio Alto, close to the funicular, walkable to the Time Out Market. The flat itself is on the top floor which was nice. It has two bedrooms, a small bathroom, small kitchen, and very small dining area.
The street noise was there, but wasn't too much of an issue.
The furnishings are sparse and this is an older apartment, nicely decorated. But you'll notice small things like soft spots in the linoleum floor, no dressers, things like that. A bare minimum of just one towel for me was provided. There is no heat or air. In the winter it got a bit chilly, but I pulled the portable radiator heater up close and was okay.
I enjoyed the place. If you want a very convenient location this is a great place.