The Aventine Hill is located near the Piramide metro stop. It's a bit of a walk up, but it is worth it. Some of the oldest churches in the city are there, and there is also the Orange Blossom garden that offers some great views of the city, and it is also a nice place to relax. Descend from the hill towards the Circo Massimo and check out the Rose Garden before you head out to see the rest of the Rome. And don't forget about the "Buco della Serratura"!