Rock-Hewn Churches of Tigrai, Ethiopia

Dotted around the north of the country are dozens of monastic retreats carved into inaccessible cliff faces. Getting to see a few of them required effort and a head for heights.

Enclaved in these remote spots, deep in Africa, Christianity took on some astonishing twists. We were thrilled to see this fresco of Jesus, the Virgin Mary and the archangels - all with black faces.

Holy men arrived here in the 5th century after fleeing persecution in what is now Syria. They brought with them their belief in the Bible and their habit of living as hermits.

Following in their footsteps, we edged along horrible cliff footholds and into the very rock itself to discover breathtaking religious artworks and relics.

We sought rational answers to explain the amazing engineering in these improbable places. But facts and myths are so interwoven here that we learned to just shrug and go along with imaginative explanations such as "angels built this".