Like many ancient cities in the Greco-Roman world, Syracuse has a number of underground sites which are a testament to the centuries of continual inhabitation the city has experienced. Each new settlement was built above the previous one, a phenomenon that often preserved ruins by obscuring them.
The largest accessible subterranean site is on the island of Ortigya beneath Piazza del Duomo. The entrance is found in the wall that surrounds the gardens of the former Archbishop’s Palace. Beneath the palace and the pavement of the Piazza del Duomo, archaeologists uncovered several archaic cemeteries, temple remains, and a vast network of aqueducts and cisterns, all from the Greek settlement. The hydraulic works were later converted into bomb shelters against the air and sea bombardments of WWII. The site is open daily (staff availability permitting) and a ticket costs 3 euros.
Perhaps the most interesting underground site is the Jewish bath, or mikvah, also on Ortigya. Bathing is an important Orthodox ritual that is used to cleanse impurities like before a wedding or after visiting a cemetery. Bathing also has a social role in Judiasm. The mikvah dates to the 5th century and was carved from the living rock more than 30 feet beneath street level. A narrow staircase leads to the first room where there are three pools with steps leading into them. There are two adjacent rooms, each featuring a single pool, probably added later to accommodate the growing Jewish community on the island. The mikvah is beneath the Residenza della Giudecca (Via Alagona 52) and can be visited Mon-Sat on the hour from 11-5. Entrance is 5 euros.
On the mainland, Syracuse has a number of early Christian sites, including catacombs. The martyr Santa Lucia was put to death in Syracuse then buried in an underground cemetery that expanded rapidly to accommodate the early Christians who coveted burial spots near a martyr. The catacomb of San Giovanni are in the same zone and together, these extensive early Christian burial sites are second only to Rome in their size.