A 21-mile bridge spanning the North Channel of the Irish Sea - from Galloway to Northern Ireland - has been proposed by a think tank.
The bridge would link Galloway to Northern Ireland
The Centre for Cross Border Studies believes the bridge could provide international rail links and ease the strain on air services.
Group director Andy Pollak admitted it would be a massive engineering challenge and would cost about £3.5bn.
However, he claimed the gains could well outweigh the costs.
The lobby group said the scheme could use either a tunnel or bridge to link the two countries.
It would see trains originating in Dublin travelling through Belfast across to Stranraer and then to Glasgow before heading 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 CCBS outlined the pros and cons of the link, which it believes could be in place by 2030.
"It struck me that the gains to be obtained from building a bridge which might cost a couple of billion across the North Channel between Scotland and Ireland would outweigh the cost," said Mr Pollak.
A similar size project, at 22.5 miles across, is the road bridge being built between Shanghai and Ningbo in east China.
"There is already a longer bridge being built but obviously it is a massive engineering challenge and a massive financial challenge," said Mr Pollak.
"But my understanding is that the Scottish government, Irish government and Northern Irish government feel that better links between Scotland and Ireland would be an unadulterated good."
He said that if Scotland and Northern Ireland worked together they might also be able to draw in European funding.
"It is just an idea - a very, very ambitious idea," said Mr Pollak.
"But I put it forward because it could be one of the triggers to the next phase of Ireland's economic development.
"And who is to say that it couldn't also be part of the next phase in Scotland's economic development?"