It was a Ravenloft adventure. The Mists brought the characters to an old manor, where restless spirits were trying to tempt them and entrap them there for eternity. The characters were separated after a while, and every room shifted to show what would tempt each of them, and then show them the punishment they deserved. The manor showed them the horrors that happened before their arrival as weird transitions between past and present, which caused players and characters to be freaked out of their wits. One of them fell to the horror of the visions (failed a Horror saving throw) and almost killed the rest of the party in his delusional state. It was awesome!