Everybody Loves a Snowman - S3-E14
Continuity mistake: Carter and Newkirk have just taken the escapees down the tree trunk to the tunnels. When they go to open it, they clear off the snow to open it. When the shot goes to a German soldier that was chasing them, the phony stump is suddenly covered over again. It would still have been visible, having just been exposed.
Answer: It's a solitary cell. Steve McQueen, star of 'The Great Escape' is known as the 'Cooler King'.