I've seen a Cave of Ghouls magic site in the same province as a Rainbow Shroud. Location, location, location...
Regarding Bogus, I once had Bogus and crowd show up outside one of my castles' gates. Took the opportunity to Wind Ride contestants from other nations (this was way back when Wind Ride was reliable absent ethereal, huge size, or decent earth magic
) to face Bogus one-on-one for a while.