Deep among the Sitka spruce and Scots pine of Dalby Forest on the southern slopes of England’s North York Moors National Park is an enormous square clearing. Muddy underfoot, with a handful of vehicles and piles of stone scattered around the perimeter, it’s unmistakably a building site, but the four concentric walls taking shape at its center make it clear that this is no ordinary undertaking. For a start, the curved structures stand over 6 feet tall yet contain no mortar. When the project is completed, over 4,000 tons of…
