Nicaragua ’s watery “Golden Route” through southern Lake Cocibolca and down the Río San Juan  is tougher to access than it was when boat service was more frequent, so you’ll need a minimum of 7–10 days to get there, get around, and get back.
Once you reach San Carlos  (by boat, bus, or small plane), public boat transportation is regular and cheap, but limited to a handful of boats per week. As a result, unless you drop a lot of cash to hire your own personal boat and driver, you may find yourself stranded on one of 36 Solentiname islands  for three days, with nothing to do but go fishing or bird- and crocodile-watching in a dugout canoe—we can think of worse.
The Río San Juan is unquestionably worth a visit, especially the photogenic fort and river town at El Castillo .
Fly from Managua  to San Carlos  in the early morning. If you really want the full-blown adventure, take the slow boat from Granada  on Monday: You’ll arrive Tuesday morning. Poke around San Carlos until the afternoon, when the boat leaves for Solentiname.
Enjoy the island artist colony of Solentiname  set in a unique area of profound natural splendor. You can hire boats to take you among the islands, enjoy scarlet sunsets, and absorb the intense tranquility of the archipelago. Return to San Carlos Thursday morning to catch the boat to Los Guatuzos. If you’d rather go directly and bypass San Carlos, strike a deal with a local Solentiname boat owner.
Hike and explore the fascinating tropical landscape of the Los Guatuzos Reserve . A two-day stay will give you a taste for the reserve, but real outdoors enthusiasts will probably prefer to stay until the next boat (Tuesday, unless you make other arrangements). Arrival in San Carlos on Saturday means you are just in time to catch a boat downstream. Cast away and start your adventure down the mighty Río San Juan , bound for El Castillo.
Start your day off in El Castillo  early, so you can hear the sky fill with birds. Visit the old Spanish fort or rent a horse for a bush trip.