It may appear to be a pipe dream to some, but the prospect of boarding a train in Belfast and waking up in Rome may only be a few years away.
A similar length bridge has been built in China
A lobby group, the Centre for Cross Border Studies, has held discussions about a plan to build a bridge or tunnel from Northern Ireland to Scotland.
A project costing up to £3.5bn could connect the Antrim coast to Galloway, 21 miles away in south-west Scotland, according to the Irish News newspaper.
It would see trains originating in Dublin travelling through Belfast, across the proposed bridge or tunnel, down through Britain and across the English channel.
Track upgrades would mean trains would be able to reach speeds of almost 200mph.
In a document, the Centre for Cross Border Studies, which has offices in Armagh and Dublin, outlined the pros and cons of the link, which it believes could be in place by 2030.
The major consideration would be the high costs and low density populations in Northern Ireland and the Republic.
A similar size project, at 22.5 miles across, is the road bridge being built between Shanghai and Ningbo in east China.
The bridge, which will have six lanes and allow traffic to travel at 100km/h, will shorten the distance between China's commercial capital, Shanghai, and the major industrial port of Ningbo by 120km.
Officials plan to open the structure next year, once feeder roads and toll booths have been completed.