Nic Birt’s presentation on rock-hewn churches in Ethiopia was held on Saturday, 29 May 2021. If you missed it or want to know more about the type of churches he talked about, have a look at these links to videos that show you examples of rock-hewn churches in Ethiopia.
Video 1, Video 2, Video 2.

Nic Birt has put some of his impressions into his own video.