Once an important Mayan trade route, the Río Dulce later became the route over which the conquistadors sent the gold and silver they plundered back to Spain. All this wealth attracted Dutch and English pirates, who attacked both the ships and the warehouses on shore. Spanish colonists constructed this fortress in 1595 to guard the inland waterway from pirate incursions. A 1999 earthquake in this region destroyed the river pier, as well as damaging portions of the fort.
If you wish to visit, rather than simply see the structure from the water, you'll need to approach the park overland rather than upriver, all best accomplished on an organized shore excursion.
Southwest of Fronteras, Fronteras, 18021, Guatemala