It's like staying in an Italian film star's swingin' 1960s weekend pad. Cool art on the walls (including portraits of Sophia Loren and Marcello Mastroianni), an excellent sound system, mood lighting, a long narrow layout with lots of places to hang out, and of course the requisite swimming pool between the dining and living rooms. There's also plenty of air conditioning, which is a big plus in summertime Rome, a comfy bed, multiple bathrooms (always a plus), a little garden out back, and of course a really great location: near the river and bridges, extremely close to the Villa Farnesina (recommended), and very close to about a kajillion trendy bars, restaurants and pizza joints. (The area gets crowded on weekends, but the apartment is down a side street and wonderfully quiet.) It was a great base from which to explore the endless layers of Rome.
About that pool: as others have noted, it's a cold-water pool, so we didn't actually take a dip. But after a long visit at, say, the Vatican, it was great to come back and dip tired toes in the sparkling, refreshing water. There's a faint chlorine smell, that's inevitable, but we got used to that quickly and it didn't diminish our enjoyment of the apartment.
A terrific find in an amazing city. Very warmly recommended.