WATCH: Each year, near the spring and autumn equinoxes, morning sunlight passes through the arch of Japan's Kameiwa Cave to create the image of a shining heart.

Twice each year, around the equinoxes, morning sunlight passes through the arch of Kameiwa Cave to create the image of a shining heart.

Shimizu Keiryū Park, in Chiba Prefecture, Japan, became a tourist destination when a 2015 Instagram post featured the cave’s enchanting effect of light, rock, and water. People describe the wondrous place as a real-life version of the kind of settings found in Japan’s Studio Ghibli’s animated fantasy films, like Princess Mononoke and Spirited Away.

Despite the park’s seeming natural beauty, the tunnel was actually a civil engineering project.

Said to have been bored through the rock in the 1600s, during the early part of the era of Japanese history known as the Edo Period, the tunnel diverted the river to irrigate rice fields. A mill once apparently stood near the site as well. Nearby, another attraction, the scenic rice terraces, Oyama Senmaida, preserve the region’s farming heritage. (See how Mochi, the traditional rice treats, are prepared.)

The name Kameiwa no Dōkutsu (亀岩の洞窟), "Turtle Rock Cave," refers to the stones in the waterfall. That name dates to 2002 and was given to distinguish the spot from another point slightly downriver, Nōmizo no Taki (濃溝の滝), “Deep Groove Waterfall.” The two sites tend to get confused, and you’re likely to encounter images of the tunnel labeled as either. Several other landmarks in Japan also include “Turtle Rock” as part of their name, but they refer to places impossible to mistake with the tunnel in Chiba.

Located in a rustic area of the Boso Peninsula that separates Tokyo Bay from the open Pacific, the park is only 40 miles from Tokyo’s center. (Visit a Tokyo hostel for book lovers.) It’s a relatively straight path by car, thanks to the Tokyo Bay Aqua-Line, which combines a bridge with one of the world’s longest underwater tunnels. Shimizu Keiryū Park falls within the municipality of Kimitsu.

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Travel site comments include plenty of visitors disappointed that the reality doesn’t always live up to the dreamlike vision captured in Kameiwa Cave’s best pictures. It’s still a lovely park, even when the light isn’t at its finest. The best views come between 6:30 and 7:30 a.m., near the beginnings of spring and fall. The fall display includes rich red leaves surrounding the cave.

The city of Kimitsu mentions an alternative for those who can’t make the narrow window for ideal viewing. In early summer, after the heart has faded, visitors to the park can see fireflies as they make their way along the raised boardwalk.

EXPLORE MORE: Ten ideas for a trip to Japan

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