Istanbul and water below the ground

During my trip to Istanbul I went to the Basilica Cistern. This is an underground storage area built by the Romans. It was forgotten about, until a Frenchman found it. I am not sure I agree that he rediscovered it, because somebody took him fishing there. It was a big cavern with water and a wooden platform people can walk on. It is nice and cool, which is good after a warm day in Istanbul. If I read by guide book right it featured in "From Russia in Love". There is a part of the film, where they bug the Russian embassy via an underground river of some sort. I just liked looking at the fishes swirling in the cool gloom.