In Raiders of the Lost Ark there was an amulet attached to the Staff of Ra. When you placed the staff in a particular place in the Map Room and the sun was in a certain position, it would shine a beam pointing directly to the hidden location of the Well of Souls.
Drzach & Suchy, the architect & cryptographer/software engineer behind the wicked Ombrae display we showed you last week, have taken the idea of light + shadows + timing + location a few steps further with their Shadow Clouds project. A written description would be complicated, but the vid explains it succinctly:
Drzach and Suchy envision their RP'd cubes being used for signage, but we think the architectural possibilities would also be cool, a la Raiders; you could get different interior projections at different times of day, depending on where the sun was. I'd start simple, with a frowny face at the start of the workday and a smiley face at quitting time.