Ofieri merchant (M1,6) who can be found near the Brunwich village on the east will be eager to participate in a race, all you need to do is talk to him. You have only one chance to beat him, so it is recommended to save the game before starting the race.
The track leads around the lake. When you're halfway there, the time will slow and barrels that you must avoid will fall on the road. For winning in the race you will receive experience points and new saddle: Ofieri Stock Saddle. It is required for obtaining the I Wore Ofieri Before It Was Cool achievement.