Tickets for the visits will be available on Blueticket from April 10, reveals Lisbon City Council in a note on social networks.

Discovered underground in downtown Lisbon in 1771, following the 1755 earthquake, this Roman structure corresponds to a cryptoportico, an architectural solution that created, in a sloping area with little geological stability, a horizontal platform to support the construction of large buildings.

Credits: Facebook; Author: @camaradelisboa;

At the beginning of the 20th century, these galleries became known as 'Conservas de Água da Rua da Prata', as they were used by the population as a cistern.

When they are closed, they have a water level of more than one metre in height, coming from groundwater that runs underground in Lisbon, and therefore a water pumping operation is necessary to access its interior.