In the north of Ethiopia, there's a town called Lalibela. They have eleven churches there. So far, not that spectacular. What makes it remarkable, is that all the churches are cut out of rock. Even more remarkable is that the eleven churches are closely placed together, making a compact constellation of similar structures - said to represent Jerusalem. The most spectacular churches are the ones that are completely cut out from the rock, free standing with only a connection at their base. There are still quite some academic discourses about the date of construction, but most people assume that the churches have been built somewhere around the 12th/13th century. The churches are still in use as places of worship, in case you might wonder.
Some theoretical/historical background on Lalibela can be read here.