The descent into the trench surrounding Bet Giyorgis is how the church is meant to be experienced — the full height reveals itself gradually as you go down. What's visible in the upper right corner is the original ground surface. That's how much rock was removed. The church isn't sunken. It was always there. Everything else was taken away.
© A. Davey from Where I Live Now: Pacific Northwest, CC BY 2.0, via Wikimedia Commons