Standing on the shore and looking out onto vast Lago de Nicaragua, it’s not hard to imagine the surprise of the Spanish navigators who, in 1522, nearly certain they were heading towards the Pacific, found the lake’s expanse instead. They weren’t too far off – merely a few thousand years – as both it and Lago de Managua were probably once part of the Pacific, until seismic activity created the plain that now separates the lake from the ocean. Several millennia later, by the time the Spanish had arrived, the Lago de Nicaragua was the largest freshwater sea in the Americas after the Great Lakes: fed by freshwater rivers, the lake water gradually lost its salinity, while the fish trapped in it evolved into some of the most unusual types of fish found anywhere on earth, including freshwater shark and swordfish. Locally, the lake is still known by its indigenous name, Cocibolca (“sweet sea”). It’s easy to be captivated by the natural beauty and unique cultures of the islands that dot the southwest sector of the lake, including twin-volcanoed Isla de Ometepe and the scattering of small islands that make up the Solentiname archipelago. On its eastern edge the lake is fed by the 170km Río San Juan, which you can boat down to the remote El Castillo, an old Spanish fort surrounded on all sides by pristine jungle. The Río San Juan and El Castillo are reached via the largest town on the east side of the lake, San Carlos, a bug-ridden settlement mainly used by travellers as a transit point. Making your way around the lake can be quite an undertaking: Lago de Nicaragua is affected by what locals call a “short-wave phenomenon” – short, high, choppy waves – caused by the meeting of the Papagayo wind from the west and the Caribbean-generated trade winds from the east. Crossing can be hell for those prone to seasickness. You’ll need to be prepared for the conditions and patient with erratic boat schedules.