The Río Dulce, Guatemala's Sweet River, spends its last stretch to the Caribbean squeezed into a rainforest gorge that can only be travelled by boat. It carries the outflow of Lake Izabal, the country's largest lake, for about 36 kilometres to the sea. Where the channel narrows, limestone walls rise as high as 90 metres, draped top to bottom in jungle: ceiba and mahogany, strangler figs, orchids and bromeliads on every ledge. Tree roots lean out over the water, and in places hot springs seep into the current at the bank. The Spanish knew this route mattered. At the lake's outlet squats the Castillo de San Felipe de Lara, a stone fort built in 1652 to keep English pirates off the lake, once backed by a chain strung across the river at night. Guatemala made the whole corridor a national park in 1955, and its warm lagoon, El Golfete, is one of the last refuges of the endangered West Indian manatee.
A journey downriver is slow and quiet, made in a long wooden lancha. Early mist hangs over the water; herons and egrets wade the shallows and cormorants dry their wings on half-sunk branches, part of the hundreds of bird species the park shelters. Here and there hot springs steam at the foot of the cliffs, warming the shallows where they trickle in. Beyond the gorge the walls fall away and the river reaches Livingston, a town at the Caribbean mouth with no road in and home to Guatemala's Garifuna, a Black Caribbean culture unlike anywhere else in the country. The river is still crossed almost entirely by boat, the same green corridor of forest and birdsong the park was made to protect.