Whistle Stop Tour
From Halopedia, the Halo wiki
Whistle Stop Tour
Whistle Stop Tour is an achievement in Halo: The Master Chief Collection. It is unlocked by beating the 20 minute par time on Two Betrayals. The achievement is worth 10 Gamerscore and can be unlocked on any difficulty.
Trivia
The achievement is named in reference to Halo speedrunner sub_WHISTLE.