Aokigahara Lava Forest Guided Nature Walk Beneath Mount Fuji in Hakone

Aokigahara is a forest with a birth date. In 864 an eruption on Mount Fuji's northwest flank sent the Jogan lava flow across the plain below, and everything you walk through here has grown on top of that rock since. Three thousand hectares of it now, dense and green and only about twelve centuries old, which in forest terms is young. That single fact explains almost everything odd about the place, and a good guide spends the walk unpacking it.

The soil over the lava is thin, sometimes only a few centimetres deep, so trees cannot push roots down in the ordinary way. Instead they spread them sideways, and the forest floor is a tangle of roots crawling over moss-covered basalt, gripping the rock like fingers. Where a lava flow ran thick, the ground is bare and hard and only certain species take hold; where it thinned or split, deeper pockets of soil allowed older giants to survive. The result is a mosaic of sharply different vegetation zones lying side by side, with isolated large trees standing in ground where nothing of the sort should grow. Once it is pointed out, you can read the shape of the eruption in the trees.

The guide works the forest at three levels. Above your head is the canopy and the light it lets through. At your feet is the lava surface, the moss, the root systems and the small ecology living in the crevices. Below both is the underground: lava tubes and caves formed when the outside of a flow cooled and hardened while molten rock kept running out from inside, leaving hollow passages that stay cold enough to hold ice well into summer. Aokigahara's caves and its wider forest carry national natural monument designations, and the whole area sits inside Fuji-Hakone-Izu National Park and within the Fujisan World Cultural Heritage listing that Mount Fuji received in 2013 for its place in Japanese art and pilgrimage.

The compasses, incidentally, really do misbehave. Fuji's basalt is unusually iron-rich and magnetised, so a needle held near the ground can swing several degrees. It is a genuine curiosity of the geology and one of the reasons walking here with someone who knows the forest matters more than it would elsewhere: the paths are subtle, the terrain looks the same in every direction, and the interesting parts are off the obvious lines.

Practically this is an easy walk, not a hike, and it starts from three hours. The ground is uneven lava with roots and low rock steps, so sure footing and proper shoes are needed, but there is no climbing and little altitude gain. You meet at Fujisan Station in Fujiyoshida and private transport to and from the forest is part of the tour. Booking is private for up to six people and the rate covers the whole party rather than each walker, so a family of five pays the same as a couple. Only personal expenses such as food, drinks and souvenirs are left out. It pairs naturally with a Kawaguchiko or Fujiyoshida stay and works in almost any season, though the forest is at its best in the green months and after rain, when the moss is fully awake.