Twice a year, a hatch in a busy Lisbon street opens to reveal steps leading to one of the Portuguese capital's most ancient sites: a 2,000-year-old Roman structure that still holds the buildings above it together.
Dating back to the first century AD, the "cryptoportico" subterranean maze of tunnels and passageways was built by the Romans, who occupied the city then known as Olissipo beginning around 200 BC. The city remained under Roman control for several centuries.
"This structure guaranteed and, 2,000 years later, continues to guarantee that the buildings above our heads are stable and safe for those who live, work and walk up there," said Joana Sousa Monteiro, director of the Lisbon Museum, as she toured the site known as the Roman Galleries.
It opens up for only a few days in April and September each year. The space is usually flooded due to an aquifer running beneath the city. The water, which is essential for its preservation, must be pumped out to allow access.
The galleries were first discovered in 1771, when Lisbon was being rebuilt after the devastating Great Earthquake of 1755.
Tickets to visit the galleries usually sell out within 15 minutes. Among the lucky ones who managed to buy one was Gustavo Horta, a Brazilian who lives in Lisbon.
"It's unmissable," he said shortly after climbing up the steep stairs out of the underground galleries. "I've waited two years to go on this tour."
