Traveling the wide, brown Sambú River is a memorable experience: you'll glide past spectacular jungle and traditional Emberá and Wounaan villages. Be warned, though, that it's not everyone's cup of tea. If riding in a boat laden with leaking gasoline cans bothers you, you should probably pass on the Sambú – you'll need to bring several large containers of gas from La Palma (where you'll arrange boats and guides for this section of the trip) to fuel the canoe you hire upriver.
This journey has other minor hardships, such as a lack of showers and toilets and an abundance of creepy-crawlies. But a trip up the Sambú is a real adventure, something that may not be possible anywhere in the tropics 50 years from now. Even if you travel deep into the Amazon, you'll be hard-pressed to find such wilderness, even now.
At night you can make camp if you have a tent or a jungle hammock. However, your boatman may prefer to make a deal to sleep on the floor of an Emberá or Wounaan family's home. If you can speak Spanish, finding a family to move in with for the night isn't difficult, and you might even get a hot meal.