Rayman Fiesta Run

Load up level 23. About halfway through the level (you'll have 65 lums if you've gotten them all), there will be a bounce pad that you'd have to jump over to proceed. If instead, you hit the pad, you'll be bounced backwards onto another pad and loop back.

You can just sit there in that loop and cycle forever. When you're done racking up the miles, jump past the pad and finish the level. (Might be worth buying the Phoenix upgrade if you're worried about dying since I don't know if the distance still counts if you die and the respawn point is immediately after the loop.)

This isn't my video, but the loop I'm referring to is at 11:53 in this video.

As there is no progress for this achievement, I don't know how long you have to sit there. The achievement will not unlock until you finish the level. After having done all of the other levels, I looped there for 30 minutes but I was probably close. I'd estimate 3 to 4 hours if you do it from scratch. Just leave it running overnight and you should be fine.

(No need to do this all in one run either.)

If you are doing this in conjunction with the rest of the achievements, you should get this as you work towards other achievements. However, if you haven't gotten this before you finished all other achievements, or if you re-installed the game after the update and have just finished the update only, you can repeat level 9, Flying Fish Tails, over and over until you get it as it is the fastest level to complete. You can complete other levels if you prefer them instead, but level 9 is the quickest.