Tako's Seven Holes

Tako no Nanatsu-ana: A Hidden Sea Cave Wonder at the Tip of the Shimane Peninsula

Where the Shimane Peninsula reaches its northernmost point and tumbles abruptly into the Sea of Japan, the cliffs hide a secret. Beneath a wall of dark volcanic rock that rises fifty meters from the surf, the sea has spent countless centuries carving out a labyrinth of caverns. This is Tako no Nanatsu-ana — literally, the "Seven Holes of Tako" — a National Natural Monument that rewards visitors willing to venture out by boat with one of the most dramatic stretches of coastal scenery in the San'in region.

Designated in 1932 and largely unchanged since the geological forces that shaped it began their work, this site is a quiet, less-touristed gem of the Daisen-Oki National Park. For travelers seeking landscapes that feel ancient and elemental, a journey along this coast offers the kind of moment that lingers long after the trip ends.

What Is Tako no Nanatsu-ana?

The site refers to a cluster of sea caves carved into the base of the cliffs that line the headland known as Tako-bana, on the north coast of Matsue City's Shimane-cho district. The cliffs themselves stretch roughly four hundred meters from the small inlet of Okidomari to Sezaki, rising as a near-vertical rampart of layered volcanic rock.

At sea level, nine cave mouths open along this rampart. From a boat positioned out on the open water, a viewer can typically see seven of them at a glance — and that, by long-standing tradition, is the origin of the name. The caves are not separate features. Inside the cliff, they connect into a single great cavern that runs roughly parallel to the coastline, with ceilings reaching anywhere from ten to twenty meters high. The largest of the openings are wide enough to admit small fishing boats, allowing visitors to glide through cathedral-like interiors where light, water, and stone interact in constantly shifting ways.

Why It Was Designated a National Natural Monument

Tako no Nanatsu-ana received its designation as a National Natural Monument on July 23, 1932 — making it one of Japan's earlier protected natural sites and a contemporary of many of the country's most celebrated landmarks. The designation was based on the site's outstanding scientific and scenic value as a textbook example of marine erosion in a layered volcanic coastal cliff.

Several qualities set this site apart from other coastal caves in Japan. The scale is unusual: a continuous cavern roughly four hundred meters long, with multiple interconnected entrances arranged in a single line, is geologically rare. The clear relationship between a major fault line and the resulting cavern formation makes the site valuable for understanding how tectonic structures guide coastal erosion. The combination of agglomerate and tuff layers also produces unique surface textures and weathering patterns that geologists continue to study today. Finally, the dramatic interplay of vertical cliffs, deep caverns, and the changing colors of the Sea of Japan creates a landscape of exceptional aesthetic merit, qualities that the original 1932 evaluation specifically praised.

The site is also recognized as a designated geosite within the Shimane Peninsula and Shinjiko-Nakaumi Estuary Geopark, a Japan Geopark Network member that highlights the geological story of how the Shimane Peninsula formed during the opening of the Sea of Japan.

Highlights to Look For

A visit by sightseeing boat from Kaga Port typically takes around eighty minutes, with the boat tracing the coastline past several smaller features before arriving at the main cliff face. Among the experiences worth savoring are the following.

• The approach by sea: The first view of the four-hundred-meter cliff wall, with its multiple cave mouths arranged like dark windows in a fortress, is the moment that earns the site its reputation.
• Entering the great cavern: When conditions allow, the boat passes through one of the larger central openings into the interior. The sudden shift from sun on open water to filtered light reflecting off cave walls is unforgettable.
• The skylight chamber: One eastern side cave has a natural circular hole in its ceiling, formed by a collapse. On clear days at the right hour, sunlight beams down through this opening, lighting the chamber from above.
• The "blue cave" effect: Local guides sometimes refer to the site as "the Blue Grotto of Japan" because of the way the water inside the caverns can take on an intense, glowing blue under the right light conditions, especially in summer.
• The U-shaped tunnels: East of the main cavern, two separate openings join inside the cliff to form a slender U-shaped passage — another remarkable example of differential erosion.
• Makuragi-ana: West of the main cavern, a separate cave called Makuragi-ana extends for several dozen meters before being blocked by accumulated gravel; its full extent remains unmapped.

Visitor Information

Tako no Nanatsu-ana is best — and arguably only — appreciated from the water. The cliffs above are part of a remote coastal headland with no tourist infrastructure, so the standard way to visit is by joining a sightseeing boat tour from Kaga Port, on the north shore of the Shimane Peninsula.

What to See Nearby

The Shimane Peninsula's north coast is one of Japan's most under-rated stretches of scenic geology and ancient mythology. Visitors traveling to Tako no Nanatsu-ana can easily combine the trip with several other notable sites.

• Kaga no Kukedo (the Kaga Sea Caves): A pair of caverns — Shin-Kukedo and Kyu-Kukedo — long associated with the birth of the deity Sata-no-okami as recorded in the eighth-century Izumo no Kuni Fudoki. These are accessible on the same boat tours.
• Tsukishima Dyke (a Natural Monument): Just east of Tako-bana lies Tsukishima, a small island whose northeastern cliffs display a remarkably complex pattern of intrusive volcanic dykes. It received National Natural Monument status alongside Tako no Nanatsu-ana.
• Sata Shrine: An ancient Izumo-style shrine in nearby Kashima, dedicated to Sata-no-okami and ranked among the most important shrines in the region.
• Matsue Castle: About thirty kilometers south, the National Treasure castle of Matsue is one of only twelve surviving original castle keeps in Japan and a worthy companion stop on any Shimane itinerary.
• Geopark Visitor Center: The Shimane Peninsula and Shinjiko-Nakaumi Estuary Geopark Matsue Visitor Center, located near Marine Plaza Shimane, offers excellent context on the geology of the region before or after the boat trip.