I stayed here in 2014, as part of a three day tour, and then for an extra two nights by myself.
To stay in the rainforest in the Amazon within Brazil you usually have to be part of a 'packaged' tour.
This lodge, Antonio's Jungle Lodge, is one of the cheaper lodges, and also the only one I know of in the region that allows a stay after the tour.
The tours themselves are 'jungle adventure' tours for budget backpackers. Which means you will likely be hiking with younger international backpackers with little wildlife experience or focus, and get a guide with stories and survival tricks, but who may not be able to distinguish between different bird species or plant families (In contrast to the knowledge of guides in the Pantanal or at the more expensive lodges). You'll fill up the day with activities such as jungle walks and fishing. Some of these activities are interesting, such as the piranha fishing, but if you are a naturalist, bird-watcher or wildlife viewer, you might get frustrated. The guides do their best, but they catering to a young crowd that may not have the patience or interest to bird-watch in the jungle. On the tour the guide will point out any monkeys high in the canopy, toucans, and if he sees a snake. Best of all, they are very good at enticing tarantulas out of burrows.
But hang in there until after the tour and you can spend a few days at the lodge. You have a choice of accommodation types here, from a communal hammock, a dorm, or separate 'chalets'. Perhaps the best rooms are those in the observation tower.
There is a trail at the back of the lodge that does a short loop. It is OK for birding in the morning or frogging/insecting at night.
The best birding is no doubt the gardens around the buildings, and if you sit at the restaurant you should see a number of good species (especially if they put some fruit out), including tanagers...
There is also the option of grabbing a canoe and going for a paddle on the river. You won't see a lot of animals this way (some birds, bats, butterflies, snakes, etc), but it is a very pleasant experience paddling by oneself on the back black-waters of the Amazon.
The website for the lodge is through: