There is something about the idea of a rail journey between different countries that sings to the soul of the traveller. The Orient Express may no longer exist as a time-tabled service, but the ghost of this connection between Paris and Istanbul still rattles along the tracks of the imagination, dashing across Europe in a blur of pre-aviation glamour.
The Trans-Siberian Railway - still very much in action - is the prime example of a great odyssey by train. And while familiarity has perhaps dimmed the allure of the Eurostar a little, it should not be forgotten that the tunnel that was carved out beneath the Channel between 1988 and 1994 was - and is - a remarkable feat of engineering.
So rumblings about a new project that would make it possible for globe-trotters to travel all the way from London to Tokyo by train is sure to pique a few interests. Not least because Tokyo, like London, is on an island. And where the Channel Tunnel - as already mentioned - has linked the British capital to continental Europe for almost three decades, no such connection between Japan and mainland Asia currently exists.
But the crucial gap in the track - between Japan and Russia - is smaller than you think. Specifically, it is 45 kilometres - between Japan's northernmost island Hokkaido and Russia's Far Eastern outcrop Sakhalin. These two neighbours have long been close. Indeed, Japan regarded Sakhalin as its own territory for much of the 19th century (before surrendering its claim to Russia in 1875) - yet there has never been an attempt to span the Sōya Strait which divides them with anything more permanent than a ferry.
Until recently. In the last two years, there have been significant mutterings from Moscow about constructing a bridge or a tunnel that would tie the two islands together - and plug Japan's rail network into its European counterpart. Two summers ago, at the Eastern Economic Forum - a pow-wow held every year in Vladivostok which attempts to encourage foreign investment in the Russian Far East - Russia's then-First Deputy Prime Minister Igor Shuvalov raised the issue as a point of international conversation.
"We are seriously offering Japanese partners [the chance] to consider the construction of a mixed road and railway passage from Hokkaido to [the] southern part of Sakhalin," he stated. "At the same time, we are close to starting our part of the job, which is extending the railway to the Pacific shore and the construction of [a] passage of the same complexity from [the Russian] mainland to Sakhalin."
This, of course, is the other obstacle to be overcome - the fact that, at present, there is no bridge or tunnel from continental Russia to Sakhalin. However, this may only be a matter of time. The issue was discussed as recently as last July, when Vladimir Putin commissioned a study on the viability of building a bridge across the Strait of Tartary - which separates Sakhalin from the Russian mainland. The strait is only 7.2 km wide at its narrowest.
Neither mooted bridge (or tunnel) - between Sakhalin and Hokkaido, or between Russia and Sakhalin - is beyond the wit of modern technology. Indeed, several projects of greater size and technical difficulty already exist. The key example is the Seikan Tunnel which allows shinkansen trains to speed between Hokkaido and Japan's biggest island Honshu.
Not only was this below-the-seabed marvel, which opened in 1988, designed to withstand the earthquakes which can be such a problem in the region, but, at 52 km, it is longer than a similar structure between Hokkaido and Sakhalin would need to be.
The Channel Tunnel - though obviously not at risk of Pacific Rim earthquakes - is, at 50 km, also lengthier. Any bridge between the islands would also be shorter than recently-built infrastructure. The Hong Kong–Zhuhai–Macao Bridge (technically a set of bridges, tunnels and artificial islands), which opened last October - linking the three named cities across the South China Sea - is a mighty 54 km long.
While Russia is clearly not suggesting the project for philanthropic reasons - the benefits of a more integrated relationship with the world's third biggest economy require little explanation - it does raise the tantalising prospect of a journey all the way from St Pancras International to Tokyo Central station without ever leaving terra firma.
Of course, we are still at least a decade away from this being possible. For one thing, the Trans-Siberian Railway line currently terminates at Vladivostok. As Igor Shuvalov commented two years ago, a high-speed track would need to be constructed towards Sakhalin for trains to go further east. And while Sakhalin does have railway lines, these would need a significant upgrade to make them fit for trans-continental services.
See also: Braving the Trans-Siberian in winter
But it may be that, by some time around the year 2030, it could be possible to climb into a rail carriage in the middle of London, and emerge from another in the Japanese capital some two or three weeks later (depending on how long you take over the process).
It would be an odyssey requiring patience and fortitude - rolling along the tracks of eastern Europe, almost certainly via Germany and Poland - and probably via Belarus (though you might also go via Lithuania and Latvia) - to pick up the Trans-Siberian at the Yaroslavsky terminus in Moscow. It would continue across the torso of European Russia, via cities with vaguely familiar names - Nizhny Novgorod, Kirov and Perm.
It would pass through the Urals, and delve into Asian Russia - pausing in Yekaterinburg, where the last tsar and his family were executed in July 1918. It would spear through Siberia, via Novosibirsk and Krasnoyarsk. It would wave goodbye to the rail-line down into Mongolia just beyond Ulan Ude - and to the junction with the line to Beijing at Tarskaya. And it would trundle into Vladivostok, where the Pacific breaks on the dockside, six-and-a-half days and 9772 km after leaving the Russian capital - where an onward adventure in search of Sakhalin, Hokkaido and Honshu would begin.
As a side-note, the construction of a bridge or tunnel between Russia and Japan might also lead to the resolution of one of the last hanging threads of the Second World War.
The two countries have been at odds over the Kuril Islands - an archipelago of 56 islands which begins just off the coast of Hokkaido, and stretches north-east into the Pacific across 1300 km of ocean - since August 1945. It was then, in the dying embers of the war, that Russia seized what had been Japanese territory.
The matter has never been formally resolved. Japan claims the four southernmost islands - including Iturup and Kunashir - as its own, and there were rumours of a rapprochement (which never materialised) during the (Russian) presidency of Boris Yeltsin in the Nineties. A joint project as considerable as building an international bridge would necessitate cross-governmental talks at a high level, and it is impossible that the disputed status of the Kurils would not be on the agenda. This fascinating topic may yet have further to run.
The Telegraph, London