The gold-diggers rout
From the Nicaragua Lake flows the great river San Juan to the Caribbean Sea. As it is navigable they planned to construct a canal here, before building the Panama Canal. During hundreds of years the pirates took this way to plunder the city of Granada. In the 19th century hundreds of thousands adventurers used this waterway rout to California to hunt gold.
Now you can take a boat from San Carlos and go down the river through deep rainforest. After a few hours you will reach the fortress El Castillo, built to prevent the pirates from going up the river. It is situated at a stream where the boats could not pass rapidly, and therefore was an easy target for the canons. Now the fortress is a museum, there is also a little hotel. But don’t stay there.
Go on to Bartola, another half-hour down the river. There is a little hotel just where the little river Bartola meets Rio San Juan. It is a wonderful place with good food and nice and helpful staff. They will take you on guided tours through the rainforest in a national park. You can even try to paddle canoe, dug out of a trunk just like in the Stone Age.
Where the Rio San Juan meets the Caribbean Sea is a village called San Juan del Norte, also called Greytown. They say the airport will soon be renovated. Then it will be possible to take a flight back to Managua, now you have to take the boat the same way you arrived.