Forza Horizon 3

To create a bucket list challenge you have to approach the appropriate blue marker on the map. The first of these points will appear after you have completed any 5 of the Horizon created bucket list challenges and you will be notified.

Once at the marker, you have the option to chose which type of bucket list challenge you would like to create (danger zone, speed trap etc) and where you would like the destination to be. You can also rename it. You then get the opportunity to set the required time/speed/distance for your challenge.

Simply create the challenge and then beat your own time to get this achievement.

(Note: The first creation marker appears near the 5th bucket challenge you complete but as you drive around the map after this, more markers will appear for other locations you can create challenges from)