On his way to founding the Lo Gekhar Monastery, Guru Rinpoche stopped at Chungsi Cave. He meditated here sometime “early in the 8th century,” says the internet, and a small monastery was later established in the cave.
To get there takes a hell of a lot of steep hiking down, followed many stairs back up. If I remember correctly, the descent from the high point of the morning hike was roughly 800 feet. It looks like there are five or six monks living up there. The monastery is very simple and is centered on the cave itself.
While the golden statue of Guru Rinpoche pictured above dominates the front of the cave, Guru Rinpoche himself allegedly slept in a small hole in the cave wall that now serves as a place to leave offerings:
