Nomizo Falls and Kameiwa Cave

A hand-dug Edo-era cave on the Boso Peninsula that a stream flows through. Around the equinoxes, early light and reflections form a heart shape.

A cave dug for rice fields

In Kimitsu, Chiba Prefecture, on the upper reaches of the Sasa River deep inside the Boso Peninsula, there is a nature park called Shimizu Keiryu Hiroba. At its heart is Kameiwa Cave, a tunnel cut through the rock that the river flows straight through.

The cave is not natural. In the Edo period, people dug a tunnel through a rocky hill in the middle of a meandering stretch of river to reroute the flow and make room for rice fields. On the Boso Peninsula this kind of work is called kawamawashi ("turning the river"). A step inside the tunnel forms a small waterfall.

"Nomizo Falls" and "Kameiwa Cave"

The place in all the photos is often called Nomizo Falls, but the original Nomizo Falls is actually a different waterfall about 50m downstream of the cave. As photos of the cave spread on social media, the two names got mixed up.

The name Nomizo is said to come from nomizo, a channel dug to turn waterwheels for farming, written with the character for "farming"; later the "water" radical was added to it, giving the kanji used today.

When to see the heart of light

The light coming in through the cave mouth and its reflection on the water can combine to look like a heart. According to Chiba Prefecture's tourism website, the best chance is early in the morning around higan in March and September (higan is the week centred on the spring or autumn equinox), for about an hour from around 6:30am.

There is plenty to enjoy at other times too. In late June Genji and Heike fireflies dance here, and in autumn you can see the leaves in the Kameyama area, said to turn later than anywhere else on Honshu. There are also walking trails along the stream nearby.

Getting there and a warning

By car it is about 38 minutes from the Kimitsu interchange on the Tateyama Expressway, and there is a free car park. By train, take a taxi from Kazusa-Kameyama Station on the JR Kururi Line, about 15 minutes.

According to Kimitsu City, the area in front of the cave, where the heart is seen best, is currently at risk of falling rocks and landslides. When you visit, follow the signs and any restrictions on entry at the site.

Tips

• If you want to see the heart, aim for early morning around higan in March and September. Outside that window the heart shape does not show clearly.
• Mamushi (Japanese pit vipers, which are venomous) and leeches can turn up around the trails. Wear long trousers and comfortable walking shoes.
• There is also a bell along the trail. Rather than just seeing the cave, it is worth walking a little way along the stream.

Sources

• 清水渓流広場（濃溝の滝・亀岩の洞窟）｜君津市 (opens in a new tab)
• 清水渓流広場（濃溝の滝・亀岩の洞窟）｜千葉県公式観光サイト まるごとe! ちば (opens in a new tab)
• 濃溝の滝 - Wikipedia (opens in a new tab)

Updated 30 September 2026. Opening hours and prices change, so check the official site before you go.