Ashizuri Submarine Museum

Ashizuri Submarine Observatory

A double-helix staircase of sixty-four steps spirals down inside a white steel cylinder and ends in a circular room about seven meters below the surface of Tatsukushi Bay. Sixteen round windows, each 60 centimeters across, open onto the sea. There is no tank, no pumped circulation, no curated set of specimens. What passes the glass is whatever the tide brings that day: butterflyfish and neon damselfish over table coral, schools of sardines when the current runs, the occasional porcupinefish drifting through.

This is the Ashizuri Submarine Observatory (Ashizuri Kaitei-kan), a fixed undersea observation tower standing offshore in the Tatsukushi Marine Park, within Ashizuri-Uwakai National Park, at Misaki in Tosashimizu on the southwestern tip of Kochi Prefecture. It was completed in 1971 and opened to the public on the first day of 1972.

The structure reads as a piece of late-1960s optimism rendered in steel. A red cross-shaped observation deck sits roughly seven meters above the waterline, and from one arm a connecting bridge of about 50 meters runs back to the rocky shore. White cylinder below, red cross above, round portholes throughout: the design belongs to the brief period when Japan imagined the sea floor might become an everyday destination.

How a 1971 tower became a cultural property

In October 2022 the building was entered on Japan's register of Tangible Cultural Properties. This is worth explaining, because registration differs from the better-known designation of National Treasures and Important Cultural Properties. Introduced in 1996, the registration system applies a lighter regulatory framework to a far wider range of buildings, often comparatively modern ones, and leaves owners freer to keep using and adapting them. It recognizes structures judged to be a model of their type rather than masterpieces in the strict sense.

The Ashizuri tower qualified under the criterion for works that set a standard of form, and it was the first undersea observation tower in Japan to be registered. Part of the reasoning is structural. The cylindrical shaft and the cross-shaped observation rooms were unified by fully welded H-section steel and outer shell plating into a single rigid body weighing about 520 tons. It was built at a Kawasaki Heavy Industries yard and floated to the site by ship rather than assembled in place.

It also belongs to a specific moment. After the first such tower opened at Shirahama in Wakayama at the end of the 1960s, a short wave of undersea observation towers followed around the Japanese coast. The Ashizuri tower was the fourth to be built. Only a handful went up nationwide, and this one remains the sole example in the Chugoku-Shikoku region.

The view from seven meters down

The water here is not aquarium-clear on every day, and that is part of the point. A transparency gauge at the entrance lets visitors judge conditions before they descend. On a calm, bright day the windows frame table coral and the red fronds of sea fans, with neon damselfish flickering blue against them. When the current is strong, even on a rough day, fish gather in the turbulence and press close to the glass. The windows are built for the pressure: two sheets of 45-millimeter tempered glass laminated together.

The tower widens as it descends. The shaft is about five meters across where it breaks the surface and broadens to roughly ten meters at the observation room below. Staff have long fed the fish daily, which is why the windows tend to be crowded rather than empty. The founding idea, printed on the early brochures, was disarmingly plain: to walk through the living sea in your ordinary clothes.

Closed for now

The observatory is not open at the time of writing. On 1 May 2026 its operator, the Kochi Prefecture Tourism Development Corporation, suspended access because the connecting bridge to the shore had deteriorated to the point of a safety concern. No reopening date has been set. The company has said it will decide the tower's future, including how the whole facility might be repaired, during 2026. The decision is bound up with an expected rise in visitors, since the area is the home of John Manjirō, the castaway who became an interpreter and whose life is set to feature in a 2028 NHK historical drama.

Anyone planning a trip should confirm the current status before traveling. The surrounding area, which is the real reason the tower was built where it is, remains fully open.

Around Tatsukushi

The observatory sits on one of Japan's most distinctive stretches of coast. Tatsukushi and the adjoining Minokoshi shore are platforms of wave-eroded sandstone, carved by the sea into honeycombs, ridges and shallow basins that draw geologists and photographers alike. The waters offshore were named Japan's first marine park in 1970, on the strength of the reef-building corals that thrive in the warm Kuroshio current.

A few minutes on foot from the tower stands the prefectural aquarium SATOUMI (Ashizuri Kaiyokan), which presents the same Kuroshio sea life in tanks and has a shop and cafe. Glass-bottom boats run over the coral from a nearby pier, the Shell Gallery (Umi no Gallery) displays shells gathered along this coast, and the Tatsukushi visitor center, Umi no Wa, makes a useful first stop for orientation. Volunteer-guided walks among the rock formations and year-round scuba diving fill out the options.

The site lies on the coast at Misaki in Tosashimizu, about ten minutes on foot from SATOUMI along a seaside path that passes several lookout points of its own.