We only stumbled across this hike because there was a photo of Cerro Chato, the lake carved into the crater of an old volcano, in our room. We hiked from Arenal Observatory Lodge for 2-3 hours, climbing straight up, over large jungle tree roots, over rocks and fallen trees, in slippery mud. It was beautiful, hiking through primary forest on the slope of a volcano, with the trail mostly by ourselves. We were rewarded with this view once we reached the top.