The Orkney Tunnel is a suggested undersea road tunnel between Orkney and Caithness

Caithness

Caithness is a registration county, lieutenancy area and historic local government area of Scotland. The name was used also for the earldom of Caithness and the Caithness constituency of the Parliament of the United Kingdom . Boundaries are not identical in all contexts, but the Caithness area is...

 on the Scottish

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

 Mainland. The expected length of it would be about 9-10 miles (15-16 km).
The tunnel, if constructed, is assumed to make landfall on South Ronaldsay

South Ronaldsay

South Ronaldsay is one of the Orkney Islands off the north coast of Scotland. It is linked to the Orkney Mainland by the Churchill Barriers, running via Burray, Glimps Holm and Lamb Holm.-Geography and geology:...

. A total bill of £100 million is mentioned.

There are also suggested plans to connect Orkney Mainland to Shapinsay

Shapinsay

Shapinsay is one of the Orkney Islands off the north coast of mainland Scotland. There is one village on the island, Balfour, from which roll-on/roll-off car ferries sail to Kirkwall on the Orkney Mainland...

.