Where's The Next Brick?

Once there was a great building. Mighty with towers, spiky with spires, a-bubble with domes. Inside it opened into gallery after gallery, vault after echoing vault, so high that human beings who set off across its marble pavements sometimes mistook its roof for the sky and the building for the world itself. And though it showed signs of many styles, and had been built by many different architects over many centuries, it had been………..