The enigmatic Castle Heterodyne, home base for the Pulper splinter group known as the Foglios, exists in an undisclosed location somewhere in the southern hemisphere of Mars. Most people figure the castle is located in the highlands around Hellas Planitia; while the good burghers of Helium have never seen it, they only know the area immediately north of Hellas. Others contend that Castle Heterodyne lurks near the polar ice cap. A handful of conspiracy theorists have suggested that the castle is mobile, moving randomly from point to point across the surface.
All that is certain about Castle Heterodyne is that neither the Boskonian madgirl Agatha Clay nor Yggdrasil's chief engineer Agatha Heterodyne have ever visited it.
- ↑ Pedants who point out that the source material had Castle Wulfenbach, not Castle Heterodyne, as the mobile castle are routinely ignored by conspiracy theorists (who point to PS 238 and astroball as "proof" that this concept has changed from its source material as well).