From the introduction: The Secret City is located inside the Dome of Knowledge, which the PCs may have encountered in area 416. The city as they saw it was just an artfully carved façade for a divination device--one to which questions could be posed and answers magically received. However, the truth of the matter is that, for all of the magic involved in creating it, the Dome of Knowledge also has a very mundane, mechanical process involved with its operation. The city is, indeed, real and filled with tiny, trapped creatures that must work to keep its divinatory powers working.