An easy and interesting day trip from Rome is a visit to the catacombs outside the city walls. The oldest of these burial places date as far back as the second century AD. Rome's catacombs are a maze of tunnels with burial niches that still hold skeletons. Some of them have early Christian frescoes, paintings, mosaics, or sculptures. Here is information about visiting the catacombs of Rome.
For those who prefer a guided tour, Select Italy's Appia Antica tour includes a visit to one of the catacombs, the tomb of Cecilia Metella, and other sites on the Appian Way (the ancient Roman road) as well as transportation from your hotel.