Underwater

If you ever have the opportunity to try it, having sex in a spa or pool can be incredibly erotic.  My husband has "sex in public" fantasies and a couple years ago we were staying in a little hotel on a road trip and we were relaxing in their outdoor spa (hot tub).  The bubbles were going.  No one was in the pool or in the spa with us.  I was horny, so I sat in front of one of the jets so the water was stimulating my clit.  Before I knew it, I was taking off his shorts. 

Having sex underwater is tricky.  It's not as comfortable as you might think, but it's something you have to try if you have a chance.