The Shack is an interesting hostel; the owners clearly just had a spare room over their bar and decided to turn it into a sleeping dorm. Said owners friendly and welcoming and are able to organize lancha tickets as well as providing information on what there is to do in Rio Dulce.
Surprisingly, this setup works pretty well for the day or two most people spend in Rio Dulce, as there is a killer view from the balcony and guests are welcome to hang out in the bar downstairs without having to buy anything to justify their presence. Overall, this is a hostel where your tolerance for the oddities of travel will determine how much you enjoy your stay.
The Location
The address for this hostel is "behind the Rio Dulce Laundromat, under the bridge" -- this is more helpful than it sounds, as there is only one bridge of note in town, plus the hostel is reasonably well-signed from the road. Despite this suspect address, and being located through a junkyard complete with (thankfully) chained-up junkyard dogs, The Shack's location is actually pretty solid, and for an extra bonus is located over the actual river. A right out of the hostel's gates takes you along one of the main streets of Rio Dulce and it's very quick to get to bus stops, restaurants, and corner stores. A turn to the left and a few minutes of walking brings you into the crowd of vendors, hawkers, and so forth that hang out around the lancha port. Go up onto the actual bridge itself for excellent views of the estuary and sunrise/sunset. Parking is available, but as it's in the junkyard, make sure they know which car is yours.
Rooms and Bathrooms
There is one dorm room and no private rooms; the eight-bed dorm has mostly singles but one bunk bed, and each has its own mosquito net. The door lock situation is a bit strange, with the last person in for the night having to padlock the door (it remains unlocked until this happens). Luckily, there are lockers in the dorm room, so at least valuables will be safe.
Bathrooms and showers are actually shared with the bar downstairs; there are male and female toilets, but this will have to be disregarded as the only shower is in the back of the female toilet. This makes more sense upon viewing. Bathrooms and showers are decently clean and have sufficient space to perform all the necessities.
Common Spaces
A balcony with hammocks and sofas is all there is for common areas exclusively to guests. It is comfortable and adequate for a bit of chilling and whatnot, but the downstairs bar, complete with regulars, is where the party really is at. Other than these two options, there are no other common spaces.
Summary
Your mileage will vary. This is a barebones (and similarly priced) hostel that is perfect for a night or two in Rio Dulce; its major draws are its price tag and its vicinity to the ferry docks.