So (adjective) that one gasps; to the extent of taking one's breath away.
息を呑むほど美しい夕日だった。
It was a sunset so beautiful it took my breath away.
その演技は息を呑むほどの迫力があった。
That performance had a power that was breathtaking.
息を呑むほどのスピードで彼はコースを駆け抜けた。
He ran through the course at a breath-taking speed.