The Green Grotto Caves are a system of karst limestone caverns between Ocho Rios and Runaway Bay, open to visitors on guided tours. The caves extend about a kilometre into the hillside, with a central chamber large enough to have been used as a dance hall in the 1950s, and an underground lake deep enough to swim in — though swimming is no longer permitted. The green tint that gives the caves their name comes from algae growing near the entrance where light penetrates.
Tours run throughout the day and take about 45 minutes. The guides are knowledgeable about both the geology and the historical uses of the site. The caves are well lit and the paths are mostly level, making this accessible to most visitors. It makes a good alternative to Dunn's River Falls if you want something quieter — even on busy cruise days, the crowds here are more manageable.