Sure, tourist websites mention the cages, but only in passing, which is insane, given the history. During the European Reformation, some radical religious folk started Anabaptism, which, get this, insisted that only willing adults should be baptized instead of dunking babies in cold water and giving them an irrevocable lifetime membership to Christianity before they can even lift their heads.
At first, Anabaptists worked by spreading their polygamist communes throughout the lands and bringing new believers into the fold. But one branch tried a more aggressive approach to spreading their ideology. Their plan: Take over the city of Munster like their patron saint was Lex Luthor. They did eventually manage to take control of the city for 18 months, but then the local bishop banded together a resistance and managed to win it back. To remind any ambitious zealots what the town was capable of, the executed bodies of the Anabaptist leaders were displayed from the side of the church's steeple in three ornate cages. Flash forward 484 years, and the cages can still be seen from the streets, right where the resistance fighters left them. Nearly five centuries later, the people of Munster still seem to think that if they let down their medieval torture cages, those pesky Anabaptists will come back out of the woodwork to strike them when they least expect it. See, now that's how you hold a grudge.