The position
White's king stands in front of its own pawn on the seventh rank. Black's king is cut off on the d-file, and Black's rook waits to give checks from the side or from behind.
The bridge
First drive the black king one more file away with a rook check on the d-file. Then bring your rook to the fourth rank.
When your king steps out and Black starts checking from behind, walk the king down the board toward your rook. When the king reaches the fifth rank, the rook interposes on the fourth: the bridge. The checks run out, and the pawn promotes.
Remember
- Cut the king off first
- Rook to the fourth rank
- Walk the king toward the rook
- Block the last check