"place them where you want", they said. But if you want a consistent world, not every placement will make equal sense. Find thoughts and inspiration on where (and why) to put the Raven's purge sites.
Beware:
Spoilers ahead
Although your GM might have an entirely different view on the world. You have been warned, though.
Weatherstone
Weatherstone is most often used as an early loredump/ treasurehunt that drags players in the campaign, so place it near their starting position. If that is not an option for you,Z27 is often picked for its position.