Seikan Tunnel Museum — World's Longest Undersea Tunnel

The Seikan Tunnel (青函トンネル) is a 53.85-kilometer railway tunnel connecting Honshu (Aomori) to Hokkaido (Hakodate) beneath the Tsugaru Strait. Completed in 1988 after 24 years of construction, it remains the world's longest undersea tunnel (23.3 kilometers of the tunnel is underwater). The Seikan Tunnel Museum, located at the tunnel's entrance near Tappi Cape, chronicles the engineering feat, the 34 workers who died during construction, and the historical importance of the Honshu-Hokkaido rail link.

The museum features a section of the original tunnel accessible via a 140-meter cable car descent (Japan's only undersea railway experience open to public). At the bottom, you walk through a preserved section of the pilot tunnel — dimly lit, dripping with condensation, and claustrophobic — giving a visceral sense of the construction challenges. Exhibits include drill heads, construction vehicles, geological samples showing the seabed strata, and videos of tunnel-boring operations.

The museum also covers the Seikan Ferry, which operated 1908-1988 until the tunnel replaced it. The ferry sank in 1954 during a typhoon (Toya Maru Disaster), killing 1,430 people — Japan's worst maritime disaster. This tragedy accelerated plans for the undersea tunnel, making the museum a memorial to both engineering triumph and human loss.