People call it the nudist beach of Madrid, a bit far but worth the trip. You'll be enjoying sun bathing and swimming next to a big lake surrounded by a forest. To get there from madrid take the M-501. Turn to your right just 100m before the , just after 49km signal (I recommend that you start to slow down 1km before so you don't have to make a sharp turn). The so-called 'nudist cove' is located a few meters before the third parking lot, on the Yelmo path. If you go explore the forest you'll see it's cruisy with some guys hanging around.