Santi Giovanni e Paolo al Celio (with Case Romane)

A 4th-century church on the Caelian Hill built over the houses where Saints John and Paul (Roman officers martyred under Julian the Apostate in 362 AD) actually lived and were killed. The church itself has a beautiful Romanesque bell tower and 12th-century porch, but the extraordinary draw is beneath it: the Case Romane del Celio — a network of 20 rooms from the 2nd to 4th centuries, with frescoes, nymphaeum, mosaics, and the actual burial shrine of the martyrs. One of the most vivid underground experiences in Rome — real Roman domestic and early Christian spaces preserved almost intact. The site is consistently rated highly on TripAdvisor and recommended by GetYourGuide as a "hidden Rome" essential. Entrance fee to the Case Romane is separate from the free church above.