El Castillo is accessible only by boat. The standard route is to fly or take a bus to San Carlos, at the southeastern end of Lake Nicaragua, and then board a panga downriver. Pangas to El Castillo depart from the San Carlos dock and take three to four hours, depending on river conditions and whether the boat stops at intermediate villages.
San Carlos can be reached by daily flights from Managua (around 45 minutes) or by a long bus journey from Granada or Managua followed by a ferry across Lake Nicaragua (up to 14 hours by this route). Flying is strongly recommended. From El Castillo, boats continue downstream to San Juan del Norte on the Caribbean coast — a further several hours of river travel for those continuing that way.