The former castle town of Aki is best known for its well-preserved samurai district and retro Nora Dokei field clock. But many people are unaware of a hidden natural gem (and awesome spot for photographers) that is just one train stop away, at little Ioki Station.
A short 5-minute walk along Route 55 will take you to the entrance of the Ioki Cave (there are a number of signs to help those who are directionally challenged).
The cave is a 40 meter long natural tunnel that was carved out by waves millions of years ago. The high walls are encrusted with fossilized shells, a memory of when this entire area was still right by the sea.
Walking on the cave opens out into a canyon, with walls completely covered with tropical ferns of over 40 varieties, which led this hidden retreat to be recognized as a National Natural Monument all the way back in 1915. A little river runs through the cave and connects with 3 little waterfalls hidden among the lush green fern forest. The mistiness of the air and deep quiet only disturbed by the sound of water falling on the rocks creates an otherworldly experience, particularly when you visit on a weekday when no one else is around.
Since the waterfall and pools of water are the reason this cave of ferns stays so lush, it is a good idea to bring a pair of waterproof hiking boots. You may be able to borrow a pair of rainboots for free at the tourist information center by the Ioki Cave parking area, but they may not have your size and availability sometimes varies depending on COVID prevention measures.
Once you have gotten your fairyland nature fix, you can exit the canyon and take a slightly different route back toward the station, which offers great views of the ocean and rows of rice paddies (just follow the signs). Alternatively, for those that want to explore a little further, keep walking for an extra kilometer until you reach Higashiyama Forestry Park. There is an easy trek up to the 360m "mountaintop" from which you will get views of Aki and the ocean beyond, along with azaleas, cherry blossoms and other flowering plants throughout the seasons.
You can find a basic map of the cave area here.