Desire Riviera Maya Resort
I had the pleasure of staying with my partner at Desire Rivera Maya Resort (located near Cancun, Mexico), and I think he summed it up best as "one of the best travel experiences" we've ever had — and we've had a lot. The couples-only resort, which is filled mostly with people "in the lifestyle" (that's swingers and other nonmonogamous types), was also clothing-optional. The rooms are upscale, the food is fresh and tasty, and the people are even better.
The majority of couples we met were 30-50, and it was a slightly more diverse crowd than some other similar resorts. (As I noted is the pattern at lifestyle resorts in the intro, most women were fluid but in heterosexual relationships.)
We got incredibly lucky and fell in with a group of people who were some of the kindest, sexiest, and most open people I've ever met in my life. I don't know if that's a regular thing that happens at Maya Riviera — finding instant lifelong friends — but I wouldn't be surprised. Nightly dance parties, late-night Jacuzzi mingling, and an all-inclusive bar help facilitate the bonding. If you want a truly unforgettable, relaxing, and adventurous experience, I highly recommend this place. (It also has a Desire Monte Carlo cruise, which sounds pretty fun.)