Photo/Illutration The Yunohama Roten Onsen open-air hot spring resort on Niijima island south of Tokyo (Erina Ito)

Were it not for signs in Japanese, visitors to an outdoor "onsen" hot spring perched on a rocky island promontory far from the capital could be forgiven for thinking they had been magically transported to the ruins of an ancient Greek temple in the Aegean Sea.

The replica is what sets the Yunohama Roten Onsen on the island of Niijima, part of the Izu island chain about 150 kilometers south of Tokyo, apart from other spas.

Mysterious-looking sculptures and statues complete the picture of the ancient world.

The spa is open 24/7 for no charge. The views at sunset and sunrise are spectacular.

The open-air bath is available to both men and women, but bathers must don swimsuits. The mildly hot sodium chloride spring water acts as a tonic to the skin, made more pleasurable by the constantly flowing sea breeze.

The hot spring facility is packed with tourists during the summer months, but on weekdays in winter locals generally have the place to themselves.

The healing sound of waves, coupled with views of the shoreline, offers a great opportunity to strike up a conversation with fellow bathers.

Keiichi Ishino, a 72-year-old fisherman, said he visits the facility every day after he strained his shoulders while out fishing.

"There was nothing here before, not even a changing room," he said. "But recently, I've noticed many foreign families."

According to Niijima village officials, the temple-like structure was built using "kogaseki" (a type of rhyolite), a local specialty of the island, when the hot spring facility was refurbished in the early 1990s. They said the spa's design was modeled after the Mediterranean coast, which is known for its stone structures.

Kogaseki is a volcanic pumice indigenous only to Niijima and Lipari Island in Italy. It can be cut with a saw, but is not only resistant to moisture but also durable. The rock used to serve as a material for building houses, warehouses and other structures.

Situated at the foot of the temple as if it were its protector is a sculpture of Moyai (not to be confused with the moai statues in remote Easter Island in the southern Pacific Ocean). Its name comes from "moyai," which in local dialect means "helping each other." Also carved from rhyolite, it constitutes one of many Moyai sculptures dotted across the island.

A key property of kogaseki is silicic acid, which is used in the production of glass. When kogaseki is melted at about 1,400 degrees, the molten liquid is transformed into "Niijima glass," which is olive in color and has a distinctive shine.

Villagers have welcomed glass artists from home and abroad since the 1980s to promote the community as the "island of glass."

At sunset, the outdoor spa turns on an entirely different look. The temple and Moyai sculptures are lit up each evening, glowing under a stellar sky with no city lights to block out the stars in the heavens.

Reaching Niijima takes about eight hours on a large passenger ferry operated by Tokai Kisen Co. from Takeshiba Pier in Tokyo, or about two and a half hours on a high-speed ferry. From Shimoda, Shizuoka Prefecture, it takes about three hours on a passenger ferry operated by Shinshinkisen Co.

A propeller-driven flight operated by New Central Airservice Co. from Chofu Airport in Tokyo takes about 40 minutes to get to Niijima Airport.