This is a Greek Orthodox Chapel called "Descendentibus Chapel." The chapel preserves the memory of Jesus, Peter, James, and John descending the mountain, after the Transfiguration, when Jesus said to them:
"As they were coming down the mountain, Jesus gave them orders not to tell anyone what they had seen until the Son of Man had risen from the dead. 10 They kept the matter to themselves, discussing what “rising from the dead” meant." (Mark 9:9–10)
This chapel was completed in 1923 and was built upon the remains of an earlier structure.