It's awe-inspiring to walk through the ruins of ancient Roman temples and amphitheaters, but to bring history to a human level you've got see where those ancient people lived. You can do that at the Case Romane del Celio.
Underneath the Basilica of Santi Givanni e Paolo, the Case Romane del Celio is a network of ancient Roman houses. There are homes from different periods – one from the 2nd century, another from the 3rd century – and for different levels of society. There are beautiful frescoed walls and a small museum displaying some of the artifacts unearthed during the excavation of the site.
The Case Romane del Celio is open Thursday-Monday from 10am-1pm and 3pm-6pm, closed Tuesday-Wednesday. Tickets cost €8 for adults, €6 for children ages 12-18, and children under 12 are admitted for free.