Corbels, keystones, newels, lintels, and other often decorative architectural elements lean against the walls and stand in tidy rows throughout this open, barn-like structure. You assume them to be practice pieces by apprentices, or perhaps rejects from on-site work, but all look like fine craftsmanship. At the far end of the halls a man stands among a ring of hanging lanterns, pinging and pounding at a block of stone, distracted by his work.