Shimizu Keiryu Hiroba

A natural park on the upper reaches of the Sasa River in the interior of the Boso Peninsula, better known by the names of its two features: Nomizo Falls and the Kameiwa Cave.

The cave is what people come for. It is not natural but man-made – the remnant of a kawamawashi, an old technique of diverting a river through a cut in the rock to reclaim the land beyond. Light entering the tunnel mouth strikes the water and, in the right conditions, the reflection and the opening together form the shape of a heart. Photographs of it spread widely on social media, and the spot has become one of Chiba's best-known.

The effect is best seen early in the morning around the equinoxes in March and September. Note that the ground directly in front of the cave, where the shape is clearest, is at risk of rockfall.

Beyond the cave, a walking path runs through the woods, and the park keeps something worth seeing in each season: new leaves in spring, fireflies in early summer, and autumn colour. Locally the fireflies are said to be at their best in late June, when both genji and heike species drift over the boardwalk. The autumn foliage here is reckoned among the latest in the whole of Honshu.

Along the path stands the Bell of Good Fortune, given to the park in 2011 and rung towards the kameiwa, the turtle-shaped rock that gives the cave its name, in a wish for luck and long life.

The paths have been left in a natural state, and there are reports of pit vipers and land leeches, so some care is needed. There is no barrier-free access and no English-language provision.

The nearest station is Kazusa-Kameyama on the JR Kururi Line, about 15 minutes away by taxi. Kimitsu City also runs an on-demand shared taxi service, which covers this area and can be booked in advance for a chosen time and pick-up point.