While at CN, this was the nature walk we discovered.
If you walk the beach to the right, go all the way up the beach past the first Riu, past the rows of beach vendors, past the next hotel and then to the last Riu, and as far as you can walk to the north end of the beach, about 3/4 mile walk from CN.
Here the clear sand beach ends and there is an area where the sand meets the grassy flats in the bay. You can wade out in the sandy trough areas along the grass and have a nice nature walk (wade).
There are lots of interesting shells to pick up and lots of tropical fish to be seen swimming, some smaller colorful ones along with some fair sized barracuda rocketing through the water. There were also some crabs and, beware, a couple of spiny urchins which won't hurt you unless you step on them.
It's kind of like snorkeling without having to choke on seawater. You can see best if you wear polarized sunglasses. Enjoy!
Thanks for posting this. I can't wait to do this on my next trip. I also love kayaking around the other side of the bay (past the resort)and getting out to see the other point. There is cool little alcoves and places to explore.