It's actually harder than it would seem to get a Turkish shave in Istanbul. We asked a waiter who recommended us via letter to his mate who runs a very busy hair salon, under the Galata Bridge.
There is a central internal corridor under the bridge, which all of the outward facing restaurants and bars have entrances on to, on the Eminonou side. It's bright green and the staff all wear green and has no other signage. It's extremely cheap too and you get a great pampering shave for about £1!
Galata Bridge, Eminonu side,
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