The Heroes' Pursuits: Fayrlund
Side quest
Skellige 
On the world map
From the journal
There are various ways to honor the gods: prayer, bloody offerings butchered on altars marked with pentagrams and donating to temples, to name a few. Skelligers, however, have their own, unique way of doing so. Since they value physical strength and warrior spirit above all else, they organize horse races in the goddess' name. Geralt decided to take part.
The goddess smiled on the witcher and saw fit for him to win the race. But this was not the end of the tournament - a final challenge awaited him on the isle of Hindarsfjall.