The place in Mechanicsburg where the aging Carson von Mekkhan with his Arella to watch life go by, and tamper with it as needed. We don't see much of the store itself, but old Carson is lounging on what appears to be the veranda of a flat associated with the shop, seemingly enjoying a comfortable retirement, when Arella brings him word that a pretender to House Heterodyne is in town. He soon learns that there are two would-be Heterodynes in town, and not long after that, learns that one of them is more legitimate than the other. This sounds like it's worth investigating.
Heliotrope Scribe and Book Works is a good example of how the people of Mechanicsburg have dealt with the rise of Baron Klaus Wulfenbach. Some time after the legendary (but very real) Attack on Castle Heterodyne and his own ascension as Big Enchilada in Europa, Klaus decided that in the absence of The Heterodyne Boys, Mechanicsburg really needed a responsible civilian government (i.e., one that worked for him). One was duly set up, but the people of Mechanicsburg made sure that the real power in town was wielded on the sly, by people staying out of the public view at places like the Scribe and Book Works, as well as the coffee house where Carson's grandson Van "idles" his time away drinking coffee. There may be other little outposts of shadow government around town that we haven't seen yet.