While Mojiko has a great deal to offer, I want to focus here on Ganryū-jima Island off the coast and the Kanmon Strait in front of the port.

We bought a one-day round-trip ticket (1日フリー券) that allows unlimited triangular travel by speedboat among Mojiko, Shimonoseki, and Ganryū-jima across the Kanmon Strait (関門海峡). It turned out to be a surprisingly thought-provoking experience.

The strait itself is about 28 kilometres long. At its narrowest point, it measures roughly 500 to 650 metres wide. The average water depth is around 12 to 13 metres, though in some places it reaches close to 40 metres.

What defines the Kanmon Strait most clearly, however, is its intense and complex tidal flow. At the narrowest sections, currents can reach 9 to 10 knots at peak strength—about 17 to 18 kilometres per hour—meaning the water itself moves at remarkable speed during intense tidal phases. Under certain conditions, particularly during spring tides or specific current patterns, measurements suggest the flow may exceed 10 knots.

These fast-changing currents are precisely what have made the Kanmon Strait both historically significant and notoriously challenging for navigation.

Even today, the strait remains one of Japan’s busiest sea lanes, with an estimated 500 to 700 vessels—cargo ships, tankers, ferries, and fishing boats—passing through daily.

Within this dynamic stretch of water lies Ganryū-jima, a small and quiet island best known as the stage for one of Japan’s most famous sword duels.

In 1612, the legendary swordsman Miyamoto Musashi fought Sasaki Kojirō here. Kojirō was associated with the Ganryū school of swordsmanship, from which the island later took its name. According to tradition, Musashi arrived late, wielded a wooden sword carved from an oar, and defeated Kojirō in a duel that became a cornerstone of Japanese martial lore—though the exact details remain debated.

Today, Ganryū-jima is uninhabited and serene, marked by statues commemorating both swordsmen. It is accessible by a short ferry ride from either Shimonoseki or Mojiko.

Beyond Ganryū-jima, another site of deep historical weight lies nearby: Dan-no-ura.

Dan-no-ura is a stretch of sea within the Kanmon Strait remembered as the site of one of Japan’s most decisive naval battles.

In 1185, the Battle of Dan-no-ura* marked the final confrontation of the Genpei War, fought between the Taira (Heike) and Minamoto (Genji) clans. The battle ended in the Taira clan’s defeat, aided by shifting tides and internal defections. The young Emperor Antoku, still a child, drowned in his grandmother’s arms along with many Taira nobles, bringing the clan’s rule to a tragic end.

This single battle reshaped Japanese history. Victory enabled Minamoto no Yoritomo to establish the Kamakura Shogunate, ushering in the age of warrior rule and diminishing the imperial court's political authority.

Today, the fast-moving waters, scattered monuments, and nearby sites such as Akamagaseki and Akamagaseki Shrine quietly commemorate this turning point in Japan’s political structure.

The events at Dan-no-ura are also immortalised in the Heike Monogatari (平家物語), a medieval war tale considered one of the foundational classics of Japanese literature. It recounts the rise and fall of the Taira clan and is central to understanding Japan’s transition from aristocratic to samurai rule.

The tale is primarily known for its opening lines, which express the Buddhist idea of impermanence (無常, mujō)—the belief that all power and glory are fleeting:

祇園精舎の鐘の聲、諸行無常の響き有り。
沙羅雙樹の花の色、盛者必衰の理を顯す。
驕れる者も久しからず、唯春の夜の夢の如し。
猛き者も遂には滅びぬ、偏に風の前の塵に同じ。

The sound of the Gion Shōja bells echoes the impermanence of all things.
The colour of the sāla flowers reveals the truth that the prosperous must decline.
The proud do not endure; they are like a dream on a spring night.
The mighty fall at last; they are as dust before the wind.
— Helen Craig McCullough, Chapter 1.1*

Watching the fast, ominous blackish-blue currents of the Kanmon Strait through the ferry windows, it is difficult not to think about the movement of time itself—about history, continuity, and the quiet question of why I am standing here today.

Sources:
Battle of Dan-no-ura - Wikipedia
The Tale of the Heike - Wikipedia