After clearing one of the 4 main temples in The Legend of Zelda: Tears of the Kingdom, you’ll be able to obtain the Who Goes There? side adventure by speaking with Jerrin at Lookout Landing in the emergency shelter.
For this quest, crouch through the hole in the wall that Jerrin created to reach the Royal Hidden Passage. Follow it to the dead end where you’ll need to use a bomb or heavy weapon to break through the rock. After breaking the first rock, head to the right to find another breakable rock wall. Tear it down to find the Horned Statue.
Speak with it and it’ll steal one of your Heart Containers. This will begin the A Deal With the Statue side adventure. Speak with the statue again and you’ll be able to choose to regain a heart or stamina. It’ll then explain that you can pay to switch your hearts to stamina or vice versa. After the explanation, the side adventure will complete! Report back to Jerrin to complete the quest. As a reward, you’ll receive a red rupee.