On the northwest side of the lake, this park was first occupied around 1300 BC, and is thought to be the largest Preclassic-era Lenca archaeological site. The main reason to visit, however, is the wildlife. The park has 6km of trails that wind through the forest over hanging bridges and on a lakeside boardwalk, providing fantastic opportunities for birdwatching.
The ruins themselves are not terribly interesting: they’re made of clay, so have been only semi-excavated, to protect them from environmental damage. The little museum near the entrance has a few nice pieces of pottery and information panels.