The new Costa Rica. The next must-surf spot. The real Central America… Whatever the phrase, the central truth remains: The secret is out on Nicaragua. And with that buzz comes the expected raucous surfer bars, Internet cafes, and expatriate communities, particularly in the country’s Pacific highlands, which offer travelers easy access from the Pan American highway and the nice respite of a handful of charming colonial towns.

But Nicaragua offers more than near-constant swells off its stunning Pacific coastline—mountainous cloud forests, huge inland lakes, and access to river-irrigated jungle lie in an inland that’s still ripe for intrepid exploration. Zone in on one such locale with a trip to the Río San Juan region.

Lately, this land has gotten a fair amount of attention—mostly thanks to the Nicaraguan government, who proposed in October of 2006 to expand Río San Juan into an 18 billion dollar rival to the Panama Canal. The project may never come to fruition, but the canal’s specter, along with the region’s sparse tourism to date, should call outdoor adventurers urgently to Río San Juan and its abutting jungles and tributaries.

The fluid waters of the Río San Juan wander for 124 miles from the southeast corner of Lake Cocibolca to the Caribbean. Farms have replaced jungle in the upper stretches of the river, but the vast 652,358-acre Indio Maíz Reserve protects the primary forest in the lower half.

Just over 3.5 miles before the Indio Maíz, the river’s sparsely populated farmlands give way to an oasis of civilization, where freshly painted, multi-colored, stilt-mounted wooden houses line the river. Children play soccer and volleyball in a small field beside the water, and travelers gaze at the hilly horizon while eating lobster-sized camarones, or river shrimp, in one of the town’s reliable—if basic—restaurants. The simple, 17th-century Castillo de la Inmaculada Concepción de María rises above the town on a steep grassy hill, built to protect Spanish Nicaragua against incursions from the coast by the British.

Most tourists on Río San Juan stay in El Castillo or one of a handful of adventure eco-lodges just upriver. Area activities include tarpin fishing in the Raudal del Diablo, or Devil’s Rapids, beside the town, and horseback riding in the hills behind El Castillo.