The Río Dulce runs from Lake Izabal, the largest lake in Guatemala, down to the Caribbean, and its last stretch is a rainforest gorge with limestone walls ninety metres high. It has always been a door, and people have tried to shut it. In 1652 the Spanish built the Castillo de San Felipe de Lara where the river leaves the lake, to keep English pirates out of Izabal, and stretched a chain across the water at night. It did not work: a raiding party sacked and burned the fort in 1686. You can walk its ramparts and towers now and look back down the river it was built to close. The way through is a lancha, a low wooden boat, and the run takes a morning.
Below the fort the river opens into the wide lagoon of El Golfete. A maze of creeks and mangroves on its northern shore, Chocón Machacas, was set aside for the manatees hiding in them. A short trail on the island there takes you under old ceiba and mahogany hung with orchids and bromeliads, with howler monkeys calling overhead and crocodiles in the still water off the path. It is the one stretch where you have the jungle underfoot instead of sliding past it. Then the river narrows and the walls climb, hung with vines, and the engine drops to a murmur while the green closes over you. Herons and egrets work the shallows, cormorants dry their wings on dead branches, and toucans and kingfishers cross the canopy. Where thermal springs steam out of the cliff the boats stop and people slip in at the seam where the hot water meets the cold current. The river ends at Livingston, which no road reaches. Its people are Garifuna, descended from Africans shipwrecked and exiled among Caribbean islanders and put ashore on this coast in the late 1700s. Cut off by sea and forest, they kept a language, a drumming and a kitchen of their own, and the boat is still the only way to them.