Narni underground is a complex of hypogea rediscovered since 1977, consisting for the most part of water cisterns and rooms used for different uses, both by the population and by monastic orders. Some of them are now open to the public.
Excavated in the rock there is an ancient cistern from the 1st century. B.C. and a room where it is possible to make a virtual tour of the Roman aqueduct of Formina, which supplied the city, and admire faithful reproductions of some tools used by the architects of the time. Thus the tourist is accompanied in the discovery of ancient hydraulics.
The most secret place of the monastic complex is reached through an insignificant door that the first explorers reopened in 1979.
A long corridor leads into a large room, the Sala dei Tormenti (so called in the documents of the Vatican Archives).
From the mid-sixteenth century (after the Council of Trent) to the mid-nineteenth century, the Holy Office or Tribunal of the Inquisition had its headquarters here.