Tintern Abbey in Monmouthshire

You're standing at Tintern Abbey, in a green valley in Wales. Right behind you flows the River Wye, which here marks the border with England. Take a good look at that huge church without a roof. It's built of Old Red Sandstone, and if you look closely, the stone shifts from purple to buff and grey. The church is around seventy metres long and laid out in the shape of a cross.