Once someone said that there is a lake near here called Du Du lake (and Du Du caves) there was no way I was going to skip that. It also just happens to be one of the most incredibly beautiful places I've ever visited.
The DuDu lagoon is located in Cabrera on the north coast of the Dominican Republic and it is a fresh water lagoon that is fed from springs somewhere nearby. What you end up with is crystal clear water inside of a massive sinkhole that is connected to another set of caves that are out of this world.
Thrill seekers will be exited to hear that you can zipline into the sinkhole portion and if you want to you can also feel free to simply jump off the side. It isn't that far but probably scary enough to keep most people from doing it.
On the other side there is a chilled out amazing spot in the shade where they have actually built a bar and some cement platforms with much more sensible jump areas (about a meter or so)
This water is perfectly clear and since you are right at the source of the underground spring the water is actually quite cold, which is great if it happens to be high noon in summer.
I come from Thailand and the part I live in has a Phi-Phi (pronounced "pee-pee") Island as well as a Pu (pronounced "Poo") island in the province i've lived for over 10 years. Therefore, when i found out that there was a "Doo Doo" Lagoon, there was no way I was going to miss it.
I tend to like fresh water moreso than salt, so this was a wonderful trip for me. It is a little far from the major tourist areas but for me anyway, i think the 1 hour drive was worth it (there are, of course places to stay closer than where I was staying, but i don't know anything about them.)