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.
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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.