I FIRST MET NINI on a cold, billowing March evening at a café in Narni, a walled medieval city built on a hilltop above the Nera River and located about 40 miles north of Rome, in the central Italy region of Umbria. The city dates to at least 600 BC and was destroyed and rebuilt more than once. It was called Narnia in Roman times, and although there is no evidence that the writer C.S. Lewis ever visited it, the town fathers wonder if it was in any way an inspiration for Lewis's The Chronicles of Narnia.

Nini looks like the stereotypical archaeology professor: He's tall and slender, with gray hair and an impassioned way of speaking.

"Give me 15 minutes of your time, and I will show you something that will surprise you," he told me.

I followed him through snow flurries, walking up the street to a church and then down several flights of steps to a locked door. When my eyes finally adjusted to the flickering light on the other side, I saw faded and peeling frescoes, painted by unknown Umbrian artists in the thirteenth and fourteenth centuries. A thighbone protruded from the floor - I later learned that it likely belonged to an unknown nobleman who was buried beneath the chapel in hopes of his obtaining a hastened trip to paradise.

"This was discovered by six boys," he said to me in Italian. When I asked who they were, he responded, "My friends and me."

THE UMBRIAN REGION is famous for the religious art in the churches and abbeys of its numerous medieval cities, masterworks from the thirteenth and fourteenth centuries - especially those created by the Vatican painter Pietro Perugino, who took his name from the region's largest city, Perugia. Those paintings served as Scripture in the ages before common people knew how to read, and they especially depict the rich Catholic history of Umbria. Many of the region's ornate churches are dedicated to the gentle Saint Francis of Assisi, because he traveled all over Umbria working miracles and preaching to the people.

But Nini's find was a former Benedictine abbey, clearly more of an archaeological attraction than a tourist mecca or a religious shrine. Once upon a time, the abbey was accessible through the Benedictine convent above it. But the convent had been abandoned for more than a century before eventually being destroyed during World War II. The entrance to the long-forgotten underground chambers was obliterated - and then a hole opened up in an old man's garden in 1979.

Up until that time, Nini had been an apprentice surveyor. But after his discovery, he followed his fortune and pursued a doctorate in archaeology. For the last 26 years, subterranean Narni has been his life. Working with paintbrushes and dental utensils, he and a volunteer staff have peeled away layers of history. They have uncovered a 2,000-year-old Roman cistern, the remains of what appears to be a house, and even the tusk of a woolly mammoth.

Today the hidden rooms are referred to as Narni Sotterranea, or "Narni Underground"; you can tour them if you make reservations in advance. The chapel's fading frescoes speak to the passage of time. The torture chamber's walls are hung with photographs of the equipment that would have been used there during the Roman Inquisition, which lasted until the 1830s. The graffiti left by the prisoners is intact.

The secrets of these rooms intrigue Nini, and he has only recently learned more about the prisoners who were once held there. Last year, he found a treasure trove of Inquisition records in the library of the University of Dublin, Trinity College. They had been carried off by Napoleon's soldiers in the early eighteenth century to be housed in various museums in Paris. But after Napoleon's fall, the Vatican retrieved what it wanted, and the rest of the material was dispersed throughout Europe. Through his research in Dublin and in archives in the Vatican, Nini determined the identities of two of the prisoners who were kept in the secret cells.

One was a bigamist, imprisoned in 1726, who escaped after strangling one of his jailers with a rope. Another was a Freemason, locked away in 1759. Though he was eventually freed, in his defiance against his inquisitors, he carved coded graffiti into the walls of the cell: a bird, a tree, a sun and a moon with human faces, and the numerals three, four, and seven. Nini interprets them as symbols of peace, liberty, and justice.

History isn't yet done revealing itself to Nini, though. In December 2005, an earthquake split open the floor of the church adjacent to the hidden chapel. Beneath the pavement were the skeletons of men, women, and children.

He showed me their remains, and as we stood in the church apse, the evening light flickered eerily. Side by side, the partially excavated skeletons grinned up from their shallow tomb. Nini grinned too. He has more secrets to decipher.