The GPS Adventure Exhibit was interesting: an indoor pseudo-cache hunt (since a GPSr wouldn't work) through a maze with various displays on aspects of caching (how satellite nav systems work, older methods of navigation, typical cache containers, hides, etc.). I thought it would be a very good way to introduce someone to caching, and it was very kid-friendly.
The HQ visit was good too. They normally try to schedule group visits on Friday afternoons, but I was only there earlier in the week so they allowed me just to pop in. They have an enormous chest full of trackables from all over the world, and some other fun stuff (the building had a giant TB tag on it for example). Everyone was busy working when I was there, so I didn't see too much else, but it was nice to visit (and get the rare icon).
I was reliant on public transport while there, so the APE cache didn't arise as a possibility, unfortunately.