Thanks Akerbeltz, just the sort of thing I was after! I'd thought I'd seen something like this in a map of Eastern Africa (although I might be thinking of Lake Victoria which is further inland) but maybe I didn't. I've just zoomed in to have a look at Istanbul, just so I've got this right, the Black Sea exits through Istanbul to the Sea of Marmara and from there out to the Aegean and then the Med? And just so my geographical knowledge is sound: there can be no other exits from the Black Sea? Just the same as a lake?