The castle's pretty easy to get lost in. The passages are the servants', and they're windy and often narrow. Luckily people are pretty generous about directions if he does get lost.
The destination is a long hall, dominated in the middle by a massive mechanical contraption, which looks as if an orrery had been repurposed to show arcane concepts rather than planets. Various maps dominate the walls. A decent number of desks are lined up in the wings of the hall, and a woman sits at a larger desk near the entrance - probably the person he was told to talk to.