Fern Grotto

Nestled on the south fork of the Wailua River, Fern Grotto is a fern-covered lava cave that was once accessible only to Hawaiian royalty. Today, visitors can reach this natural geological formation by boat as part of a river cruise. After docking at the Fern Grotto landing, a short nature trail winds through the dense rainforest, leading to a viewing platform. Here, visitors can admire the lush, green ferns cascading from the cave’s ceiling, creating a serene and otherworldly atmosphere.