In The Legend of Zelda: Tears of the Kingdom, you can obtain The Beast and the Princess side adventure from Penn at the New Serenne Stable after starting the Potential Princess Sightings side adventure.
For this side adventure, you’ll need to travel to the Lakeside Stable, which is north of Ubota Point. Once there, speak with Shay who can be found outside by the fire.
He’ll tell you of a girl to the north just on the other side of the ravine. Make your way north to the southern part of Bronas Forest.
Speak with Cima to complete the quest.
