“A castle is built from fired brick, wood, and of course stones. So far, so good. But since not every stone fits the next, the masons have to lend a hand. They especially hammer and chisel away at the sandstone being delivered for the castle. This material is used to make almost everything the client desires: steps and windowsills as well as precious columns and statues. Masons are proud people, and some of them leave something like their personal signature on particularly well-crafted stones: the mason’s mark. We copied a mark just like that and hid it. Can you find it?”