Akiyoshido Cave

Akiyoshido is the drainage system beneath Akiyoshidai, a limestone plateau in western Honshu where grey rocks stand out of the grass like a scattered herd. The cave is the largest in the country, and roughly a kilometre of it is lit and walkable, following an underground river through chambers wide enough to lose the ceiling in shadow. The best known formations are Hyakumaizara, a slope of shallow rimstone pools stacked in terraces, and a tall flowstone column near the middle of the route. Air temperature stays close to seventeen degrees all year, so the cave is warm in winter and a relief in August. The plateau above has its own paths.

What you actually see

• Hyakumaizara - terraces of shallow rimstone pools stepping down the cave floor.
• The main passage - a lit walkway beside the underground river through very large chambers.
• The flowstone column - a tall calcite pillar standing near the middle of the route.
• Akiyoshidai plateau - the karst grassland above, with limestone outcrops and walking paths.

When to go

The cave works in any season and is a sensible choice in the summer heat or on a wet day, since the temperature inside barely changes. The plateau above is best from spring to autumn, and the grass burning in late winter leaves it black for a while. Weekday mornings avoid the school groups, which arrive in large numbers.

Honest expectations

It is a show cave: paved paths, handrails and coloured floodlighting on several formations, which some find garish. Surfaces are permanently wet and slippery, and the route has stairs. Getting there without a car means infrequent buses and a long day. The scale is real but hard to photograph, and parts of the site feel dated.

Nearby

The Akiyoshidai plateau directly above, the city of Yamaguchi to the south and the coast at Hagi to the north.