Every inch of its walls is covered in magical frescoes depicting what the 19th Century Bulgarians imagined hell to be: devils wielding scimitars, sinners boiling in tar, and God administering justice from the signs of the zodiac.
It was founded in the 9th Century by a monk who swallowed herbs and potions to embalm himself while he was still alive. His left arm is still preserved - and the abbot may let you see it on high holidays. In 1943 the last Bulgarian king was buried there. The Communists removed the grave after the end of the Second World War for fear it would become a place of pilgrimage. It is by far the largest Bulgarian monastery, a major tourist attraction in the Southwest. You can even crash there, as a monk will gladly let you hire a room for the night. It's not five-star accommodation, like the place where you will be going if you guess this location correctly, but definitely worth the effort as it entails crawling through a very low door if you have missed the 8 pm curfew, and observing the ancient rites the monks still perform. In the morning your body and spirit will be awoken by church bells.