Presidente Figueiredo is a popular starting point for eco-tourism in Manaus area. You should go to a local tourism agency and choose what you want to see and take a taxi with a guide. There are plenty of streams,
waterfalls, caves, and as it is all in the Amazon jungle, of course it is easy to find a place where you can just take off your clothes to get relief from the sweat (otherwise you will be doomed to have this unpleasant feeling of wet clothes on you, as it is so humid that without free access to the air, sweat just stays on you). Water in main rivers (Amazon, Rio Negro) is either murky or muddy, so if you want clear water you better stick to small streams.
In any case, this is the right place to feel the power and diversity of wild nature: in this giant forest you can see yourself, human, as just one of many particles of nature.
Just don’t go too far without your guide!
If you go by boat from Manaus in any direction, you will see that the Amazon river provides plenty of sandy beaches, many of which can be your private for a while!
I imagine that to most urban dwellers an idea of swimming in the Amazon sounds crazy, but actually you would rather spent many hours looking to see a crocodile or another beast, so probably it is safer than crossing a street in Rio de Janeiro. In fact, you can also find another, much more pleasant company in those waters – river dolphins botos!
In Novo Airão there is a restaurant on the river shore where you can buy fish cut in pieces and feed the dolphins while swimming together with them. This is one of the most incredible contacts you can experience with wild animals!
On the whole, the Amazon region is surely the right place where a naturist can feel unity with nature.
But on the other hand, some distant spots of the river (not in the vicinity of Manaus, if you go further, you should ask about that) might be the only place on Earth where it really makes sense to wear swimming suit, and the tighter, the better: a small parasite fish candiru can swim into the vagina, anus, or even the penis — and deep into the urethra. However, it’s also worth mentioning, that there has been only one documented (but still questionable) case of such an incident decades ago… For the rest, it is of course just fantastic place for any naturist and naturalist.