These deep, kilometres-wide channels, known as tunnel valleys, were cut by fast-flowing rivers that ran under Northern Europe's ancient ice sheets.
Today, the landforms are all hidden by the North Sea's bottom-muds, but new survey work has traced their outline in remarkable 3D detail.
Scientists say the channels should give us clues as to how modern-day ice sheets, such as Greenland, will decay.
That's because these features were all incised during periods of great melt.
"These tunnel valleys were formed during the death throes of an ice sheet in extremely warm climates," said James Kirkham, from the British Antarctic Survey (BAS) and Cambridge University.
"This makes them a great analogue for what Greenland, or even Antarctica, might begin to look like in the future, perhaps several 100 years down the line," he told BBC News.