Fern Grotto

Fern Grotto is a fern covered, lava rock grotto located on the south fork of the Wailua River, which is on the eastern side of Kauai in the Hawaiian archipelago. Several boat companies give river tours which lead to the grotto. This attraction is known primarily as the most romantic spot on the island of Kauai, and the area can be rented for weddings.

Source: Wikipedia