I first thought of the Barbara Hepworth museum in St Ives, Cornwall. The stripped-back matt white walls and bright halogen lights form a genuine art gallery, with well chosen, interesting sculptures and paintings. It forms a counterpoint to the ages-old Rome outside. There are some exceptional eating places in the square outside (especially La Carbonara, Meranenga Rome and the Bakery).
The flat is in walking distance of all of Rome's famous hills and steps.
The square outside - Campo de'flori - has a lively market most days, live music every evening. The flat has double glazing if you want this to be optional.
Luigi was very helpful, fast to respond to in-app messages and spoke English perfectly. The Espresso machine was appreciated.