Beneath the city's streets and squares which thousands of people walk through every day, there hides a wealth of history and archaeology, only part of which is visible to us. There is an unseen Bologna, an underground Bologna which is no less fascinating than the one on the surface. It can be discovered not just by strolling through the historic center, but above all by venturing underground with guided group tours of the canals that once crisscrossed the city. Among the most interesting sites are the Bagni di Mario cistern, the Salaborsa archaeological excavations, the aqueducts under the Fountain of Neptune and the Aposa stream, and the air-raid shelters.