Designed by Brazilian modernist Oscar Niemeyer, Lebanon’s international expo site has been abandoned since civil war broke out in the 1970s

“It could collapse at any time,” says the architect and activist Wassim Naghi. The facade of the unfinished, subterranean space museum in Tripoli, Lebanon, is visibly decaying and its steel reinforcements are rusted – but that may not be its biggest problem. “The ageing concrete’s carbonation is invisible,” explains Naghi when we meet in his office in the centre of the city. “We don’t know how bad it really is.”

Situated beneath an elevated concrete helipad, the museum was part of a planned permanent international fair designed by the Brazilian architect Oscar Niemeyer in the early 1960s that was expected to accommodate more than 2 million visitors a year. The 100-hectare (250-acre) site’s 15 existing buildings also include a domed theatre, an atrium, an arch and collective housing. A 717-metre-long boomerang-shaped canopy was designed to house the permanent exhibition, alongside a separate, traditionally styled pavilion for exhibitions relating to Lebanon.