The subterranean basilica beneath Porta Maggiore, Rome

Discovered in 1917, this ancient religious monument lies beneath Porta Maggiore in Rome. It dates back to the 1st century BC and is believed to have been the meeting place of the neo-Pythagoreans, a Hellenistic school of philosophy. Known for their asceticism and mysticism, the neo-Pythagoreans were notorious, with their leader, Titus Statilius Taurus, accused by the Senate of 'addiction to magical superstitions'. After years of restoration work, the basilica was accidentally discovered during the construction of a railway line. Today, it is open to visitors, albeit in restricted numbers due to the fragility of the monument. The temperature and humidity are carefully controlled. Visit during the 2nd and 4th Sunday of every month and explore this hidden underground structure,

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons