Transfer to Managua airport and fly to San Carlos (1hr) on the south-eastern shores of Lake Nicaragua. The liveliest part of this quiet and somewhat ramshackle town is down by the pier: ferries and private launches jostle for space with fishing boats. The roads from the north end here: to travel east to the settlements along Rio San Juan you have to take a boat. (New roads are opening all the time including, in 2014, one to Costa Rica which will cross the river close to El Castillo: some of the remote atmosphere in those vehicle-free towns will surely be reduced as a result).
You’ll embark on a 90min river journey by river. The banks are initially farmed, with fields of maize and grazing cattle punctuated by small jetties and rural homes. However, as you travel downstream, the vegetation gradually becomes dominated by natural tropical forest. There’s plenty of wildlife to be seen: scores of snowy ibis alight upon the branches overhanging the water and you may spot monkeys swinging through the taller trees or a caiman lazing on naked logs.
You turn a bend in the river to be greeted by a spectacular and unexpected sight: on a rare hilltop a vast, stone-built Spanish fortress glowering over a series of white-water rapids and the squat, wooden stilted houses of the quirky little port El Castillo.
In the evening, go searching for caimans by boat under the moonlight, accompanied only by a specialist guide. As you glide for 90mins through the darkness, a journey orchestrated by the nocturnal sounds of the rainforest, the guide will be using a spotlight to reflect the beady red eye of caimans (alligators) at repose in the tropical vegetation along the water's edge.