The Crowned Beast
The Crown Beast is a Shrine Quest given to Link by Kass the Rito.
At the north edge of the Rabla Plains in the Lanayru region, you will find Kass. After speaking to him, he will sing to you a legend about a beast who wears a crown of bone.
Find a Stag in the nearby field, sneak up on it, and mount it. Soothe it until it has calmed down, and then ride it back to Kass and stand on the glowing platform. This will cause Mezza Lo Shrine to rise up just north of you.
See also our guide for the Mezza Lo Shrine, nicknamed the Ancient Trifecta.