The Navigator: A Medieval Odyssey (1988), directed by Vincent Ward.
The location is a desolate copper mining village in the north of England in the Black Death year of 1348. The plague has not reached them yet, but they know it jumps ahead every full moon. What can they do?
The boy Griffin has prophetic dreams and he leads the miners on a vision quest to dig through the center of the Earth and erect a copper cross on a cathedral steeple they will find on the other side of the world. It is a race against time: they must complete their mission before the full moon or all is lost.
Griffin also dreams that one must die so that the others may live.
Dig they do, and come out in modern New Zealand, marveling at what they find: "It must be God's city, there's so much light!" Friendly men working the last night before their foundry closes help them cast their cross and get it to the church.
I will leave it there. A review cannot do justice to the wildly disorienting nature of the tale or its double-twist ending.
The stark photography for medieval Cumbria is gorgeous; the color in modern times seems more conventional by comparison. The cold, bitter realism of the former part reminds me of similar efforts in Winstanley (1975), a historical reenactment.
Available on Blu-ray from Arrow.