This unique quest will give you the chance to control Ciri for a moment. It starts automatically during the main quest Family Matters. More specifically, it starts after you tell baron Philip Strenger from the Crow's Perch (M3,3) information about his wife and daughter. In return, baron will tell another part of Ciri's story.
The quest itself is very short and not complicated. You must participate in a horse race with the baron. The finish line is at the Abandoned Tower. After the race begins, start a gallop and then full gallop. Remember that you must remain on the main path. The horse that Ciri uses should have enough durability for the whole race. Whether you win or lose the race with the baron, it will have no impact on further events. Soon the game will allow you to continue the main quest Family Matters.