Not surprisingly, a visit to Las Nubes is all about the water. The eco-center maintains an observation tower and hanging footbridge, both affording dramatic views of the riotous rapids. There’s also a 50-meter-high zip line (US$4.25 per descent) set up to whisk guests across the river in a heartbeat (or two, if the first one skipped).

There are also several hiking trails near and along the river; the trails are easy enough to navigate on your own, though you may see and learn more with the help of a guide (US$8.50/hr, up to 8 people).

Believe it or not, there are also some lovely and safe areas for swimming. Playa Las Iguanas is an attractive sandy beach fronting a stretch of river, and an easy walk from Las Nubes. It’s part of a new and separate ecotourism project, with plans to construct cabins and a restaurant as well; a nominal admission fee may be charged to use the beach once the buildings are completed.

White-water rafting is a popular and natural activity here, as well. Gallo Giro (Montes Azules Trópico Gallo Giro Centro Ecoturístico, tel. 963/633-4284) offers kayak and rafting trips from its riverside base a short distance upstream. Trips typically end at Las Nubes, and start either at Gallo Giro itself (US$50, 1 hr, 2–7 people) or upstream at the town of Jerusalén (US$85–110, 2.5 hrs); the latter includes more challenging white water (up to Class III) and a short nature walk along the way. Kayak rentals (US$8.50/hr) and eerie nighttime rafting and walking tours (US$18–25, 2–4 hrs) also are available. Ask the Las Nubes receptionist to call for reservations and arrange a pick-up. Or you can walk—it’s a pleasant 4.5 kilometers (2.75 miles) from Las Nubes along the main access road.