We happened upon the Villa Borghese as we were searching for somewhere with Free WiFi. Which it does have, provided you have and Italian mobile phone number (SIM card. After quite a bit of walking around we found the Riscio rental. For 10 Euro/hr you can rent one. This is a pedal-driven, motor assisted, bike/cart contraption that made exploring the park a blast.
After a quick lesson from the rental stand we were off into the park. The park is huge. There are lots of fountains, statues and of course the Borghese house/mansion thing. It takes a little while to understand how the riscio works, but when you figure it out, it's great. It has a motor attached that will automatically help drive the cart up hills or just keep up speed. My wife, who is not into anything that has a motor or can go quick, really enjoyed it as well.
After three solid days of lots of walking and sight seeing, we relished the opportunity to slow down, and enjoy something not in ruins.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC