This lost landscape, where hunter-gatherer communities once lived, was swallowed by rising water levels at the end of the last ice age.
University of Birmingham researchers are heralding "stunning" findings as they map the "best-preserved prehistoric landscape in Europe". This large plain disappeared below the water more than 8,000 years ago.
The Birmingham researchers have been using oil exploration technology to build a map of the once-inhabited area that now lies below the North Sea - stretching from the east coast of Britain up to the Shetland Islands and across to Scandinavia.
"It's like finding another country," says Professor Vince Gaffney, chair in Landscape Archaeology and Geomatics.
It also serves as a warning for the scale of impact that climate change can cause, he says.
Human communities would have lost their homelands as the rising water began to encroach upon the wide, low-lying plains.
"At times this change would have been insidious and slow - but at times, it could have been terrifyingly fast. It would have been very traumatic for these people," he says.
"It would be a mistake to think that these people were unsophisticated or without culture... they would have had names for the rivers and hills and spiritual associations - it would have been a catastrophic loss," says Professor Gaffney.
As the temperature rose and glaciers retreated and water levels rose, the inhabitants would have been pushed off their hunting grounds and forced towards higher land - including to what is now modern-day Britain.
The rising water levels began to remake the coastline. "In 10,000 BC, hunter-gatherers were living on the land in the middle of the North Sea. By 6,000 BC, Britain was an island. The area we have mapped was wiped out in the space of 4,000 years," explains Professor Gaffney.
So far, the team has examined a 23,000-sq-km area of the sea bed - mapping out coastlines, rivers, hills, sandbanks and salt marshes as they would have appeared about 12,000 years ago.
And once the physical features have been established, Professor Gaffney says it will be possible to narrow the search for sites that could yield more evidence of how these prehistoric people lived.
These inhabitants would have lived in family groups in huts and hunted animals such as deer.
The mapping of this landscape could also raise questions about its preservation, says Professor Gaffney - and how it can be protected from activities such as pipe-laying and the building of wind farms.