I was in Koktebel, Crimea (Ukraine) when I was a kid. It was a naturist's paradise.
Unfortunately, the Ukrainian territory of Crimea was annexed by the Russians in 2014. Unlike Ukrainians, Russians are not open to naturism, so they may change the place.
Also, there is not possible to visit Crimea legally in this time (it is now impossible to travel to Crimea from Ukraine. If you travel to Russia and then fly to Crimea, you will violate the Ukrainian's law).