I just watched an episode with Rick Steves on bicycle to the catacombs (San Calisto?) and on the Via Appia. Can I rent a bike in the city center and actually ride to these sites? Any info on renting/logistics is greatly appreciated!
I would not recommend renting in city center and riding there. To much traffic. Traffic is restricted to buses, taxis, and some locals on Sunday which is the only day to ride it via a bike. This is a bike rental right at the bus stop so that is where I would get my bike.
One other thing to consider is that even if you avoid traffic by bike-riding on a Sunday, the road itself is bumpy and you will need to constantly steer around pedestrians, other bike-riders, and the occasional horseback rider.