In order to unlock this hidden challenge you need to find or purchase the 1983 DeLorean DMC-12 and hit 88MPH with it. When you break the 88MPH, yellow trails begin to appear from the vehicle and a second or two later it'll trigger the unlock for the Blast from the Past challenge, which is a challenge set in a 1971 Pontiac LeMans in Driver 1's Garage Level.