Firstly, where IS Slovenia? Well, it's between Croatia and Austria, Think NE Italy and over a bit! Lake Bohinj has several stoney beaches on the north shore. You can park in the main lakeside car park at the eastern end of the lake, and then walk around the shore to the north shore - maybe a 15 minute walk.
As you move further away from the family beach areas, you will find several little secluded beaches. People go nude there and swim in the lake, which is beautifully surrounded by mountains.
There is a bar/cafe by the car park - parking costs €1 an hour - but no other facilities.
(This report from a guest writer - ooh, the first!)