These subterranean cisterns date from early Byzantine times but were only rediscovered in the 16th-century by visiting Frenchman Petrus Gyllius. The explorer had little time for the ‘Carelessness and Contempt of everything that is curious in the inhabitants [of Istanbul]’ and went poking around in cellars instead. He found this 6th-century part of the Byzantine’s complex, an impressive cistern system that housed the city’s reservoirs of water, together with a few odd-looking fish whose descendants still swim between the columns today. Most visitors will already be familiar with the cavernous column-strewn passages as they feature in the Bond film From Russia With Love as MI6 agent Kerim Bey’s escape route from the Soviet Embassy. Queues for the cisterns snake around the block at peak times, but their eeriness and sense of discovery makes it well worth the visit.