English
Deutsch
Español
Français
Italiano
Nederlands
日本語
한국어
简体中文
繁體中文
Somewhere beneath the waves of the Tsugaru Strait, a bullet train is quietly crossing from one Japanese island to another without a single passenger getting wet feet. The Seikan Tunnel makes that possible: an undersea rail tunnel linking Honshu and Hokkaido, and one of the longest and deepest rail tunnels anywhere in the world. Our latest JRPass guide covers the engineering, why it was built, what the crossing feels like today, and what it means for anyone travelling to Hokkaido by rail.
Special update: You can now buy single rail tickets for Japan’s Golden Route on JRPass.com - single fares, one-way, fully digital, including the Shinkansen 'bullet' train.
Quick Answer — What Is the Seikan Tunnel?
The Seikan Tunnel is the undersea rail tunnel connecting Honshu and Hokkaido beneath the Tsugaru Strait, ranking among the world's longest and deepest rail tunnels. It runs for roughly 54 kilometres in total, with an undersea section of about 23 kilometres running under the seabed itself. 
Opened in 1988 after decades of planning and construction, it now carries the Hokkaido Shinkansen alongside freight services, replacing the ferry crossings that once linked the two islands. In practical terms, this tunnel is why a train can carry you from Honshu to Hokkaido in one continuous journey. Before looking at what the crossing feels like today, it helps to understand the scale of what was actually built.
The Engineering Feat
At roughly 54 kilometres long with a 23-kilometre undersea stretch, the Seikan Tunnel's headline figures explain why it draws engineers and rail enthusiasts alike. Britannica lists its core statistics as:
- Total length of around 54 kilometres end to end
- An undersea section of roughly 23 kilometres running beneath the seabed of the Tsugaru Strait
- A track level reported to sit around 100 metres below the seabed and roughly 240 metres below sea level
These figures vary slightly between sources, so treat them as close approximations rather than a fixed spec.
The timescale is less disputed. Planning stretched back to the late 1930s, geological surveys ran through the 1960s and 70s, and the main tunnel was not holed through until the mid-1980s. Workers battled flooding, unstable volcanic rock, and a strait known for strong currents. The result, opened in 1988, was a dual-gauge tunnel built for both conventional trains and, later, the wider-gauge Shinkansen.
Why It Was Built
The short answer is that ferries were not safe enough. Before the tunnel existed, crossing the Tsugaru Strait meant taking a boat, and the strait's currents and sudden storms made that genuinely dangerous. A ferry disaster in the 1950s, in which more than a thousand lives were lost during a typhoon, turned public and political opinion firmly toward a permanent underground solution.
That tragedy pushed Japan's national railway authority to study a tunnel seriously rather than treat it as a distant idea. Decades of surveying and construction followed, but the motivation stayed constant: give Honshu and Hokkaido a crossing that bad weather could not shut down or endanger.
Riding Through It Today
For a passenger, the tunnel is mostly an experience of sound and time rather than sight. It's the Hokkaido Shinkansen that does the work, gliding from Honshu into Hokkaido without anyone on board needing to give it a second thought. A few things to expect during the crossing:
- The crossing itself takes roughly 20 minutes at current operating speeds, though this varies with the specific service.
- Windows show nothing but tunnel wall for the full crossing, so there is no view to speak of.
- The ambient hum shifts slightly through the deepest section, then daylight returns as you emerge on the other island.
- Mobile signal can drop out briefly underground, so it is worth saving maps or tickets offline beforehand, especially if you're leaning on pocket Wi-Fi to stay connected around Japan.
It is a strikingly ordinary few minutes for something so historically significant. Once you're through, onward travel around Hokkaido often mixes Shinkansen with conventional lines, where IC cards and Limited Express fares come into play.
The Tunnel and Your JR Pass
For pass holders, the crossing forms part of a route covered by the Japan Rail Pass, since it runs along the standard Hokkaido Shinkansen line rather than a separate, extra-fare service. If your itinerary already includes a Shinkansen journey between Honshu and Hokkaido, the tunnel crossing does not require a separate ticket beyond the usual Shinkansen fare and seat reservation rules.
First-time travellers heading straight north are often torn between a nationwide pass and a regional one, and weighing the JR Pass against regional options usually settles which makes more sense for the trip. Landing at a major airport before that journey is also where having someone meet you right at arrivals can take the edge off a first trip to Japan.
Records and Rivals
Precision matters here, because "longest" means different things depending on what is being measured:
- Longest undersea section: The Seikan Tunnel is generally described as the longest tunnel in the world with a section running under the sea, since its roughly 23-kilometre undersea segment is longer than the undersea portion of the Channel Tunnel between the UK and France.
- Longest railway tunnel overall: The Seikan Tunnel held this record until the Gotthard Base Tunnel opened in Switzerland in 2016, after which it became the second-longest railway tunnel overall while keeping its undersea record.
These distinctions can shift as new tunnels open elsewhere, so treat any specific superlative as something to verify first.
What's Next Under the Strait
The Seikan Tunnel's story is not finished. A few open questions worth knowing about, as outlined in Japan Railway Construction, Transport and Technology Agency's own project documentation:
- Speed: Shinkansen trains currently pass through at a lower speed than they reach elsewhere on the network, largely because the same tracks are shared with freight trains, and running both at full Shinkansen speed raises safety questions that are still being worked through.
- Holiday speed-ups: Operators have experimented with running Shinkansen services faster during specific holiday periods when freight traffic is lighter, alongside an ongoing, publicly discussed ambition to raise the standard operating speed more permanently.
- The Sapporo extension: Plans to extend the Hokkaido Shinkansen further north to Sapporo, and to resolve the freight-sharing question more fully, are best treated as evolving rather than settled, since target dates have shifted before.
If you're timing a trip around stays in Sapporo, Hakodate, and Hokkaido's other main stops, that's worth mapping out next. Anyone planning around a future timetable change should also check JR Hokkaido's page on the tunnel before locking anything in.
Frequently Asked Questions
Read on for answers to the questions travelers ask most frequently.
Q: What is the Seikan Tunnel?
A: It is the undersea rail tunnel connecting Honshu and Hokkaido beneath the Tsugaru Strait, and it is among the world's longest and deepest rail tunnels.
Q: How long is the Seikan Tunnel?
A: It runs for roughly 54 kilometres in total, with about 23 kilometres running beneath the seabed, though you should confirm the exact figure with an official source if precision matters.
Q: How deep is the Seikan Tunnel?
A: Reports place its track level at around 100 metres below the seabed and roughly 240 metres below sea level, making it one of the deepest rail tunnels in the world.
Q: Is the Seikan Tunnel the longest undersea tunnel?
A: It is generally regarded as the longest tunnel with an undersea section, though which tunnel counts as "longest" changes depending on the measure used.
Q: How do trains get to Hokkaido from Honshu?
A: They travel beneath the Tsugaru Strait through the Seikan Tunnel, which the Hokkaido Shinkansen now uses as part of its regular route.
Q: Is the Seikan Tunnel covered by the Japan Rail Pass?
A: Yes, since the crossing runs along the standard Hokkaido Shinkansen route, it is covered under normal Shinkansen usage rules rather than a separate fare.
Q: How long does it take to cross the Seikan Tunnel by train?
A: The crossing takes roughly 20 minutes at current operating speeds, though this can vary slightly by service.
Q: When did the Seikan Tunnel open?
A: It opened in March 1988, following several decades of planning, surveying, and construction.
Q: Why was the Seikan Tunnel built?
A: A ferry disaster during a typhoon in the 1950s exposed how dangerous crossing the Tsugaru Strait by boat could be, pushing Japan toward a permanent underground route instead.
Q: Do freight trains also use the Seikan Tunnel?
A: Yes, freight trains share the same tracks as the Hokkaido Shinkansen, which is one reason Shinkansen speeds through the tunnel remain lower than elsewhere on the network.
