Two volcanoes rising out of a freshwater lake, joined by an isthmus: that is the island, and it is also the list of things to do. Concepción is the perfect cone on the northern half, an eight-to-ten-hour return climb, hot and exposed near the top. Maderas on the southern half is lower, wetter and harder underfoot — cloud forest, deep mud, and a crater lagoon at the top you can wade into. Guides are compulsory on both, and worth having on Maderas whatever the rule says.
Between them the Istián channel runs through mangrove and reed, and paddling it at dawn is the quietest thing on the island: caimans, turtles, and more birds than anywhere else in Nicaragua outside the Río San Juan.
The rest is gentler — the spring-fed pools at Ojo de Agua, the petroglyphs on the Maderas slopes, and plantation roads that are ideal on a bicycle and punishing on a scooter.