Ioki Cave

Steps from the roadside in Aki, a 40-meter tunnel with fossilized shells embedded in its walls opens into a hidden fern canyon hosting over 40 species in a perpetual 20-degree microclimate. The cave formed as ancient seabed pushed above the waterline three million years ago, and the fern colony was designated a National Natural Monument in 1915. Five minutes' walk from Ioki Station on the Gomen Nahari Line.