I once ran a D&D game as a sort of one-off at the end of my friend’s campaign. I had advanced the timeline a hundred years or so and the characters who were still alive were all around 30th level or so. (The players who’s characters had no excuse to be so long-lived played their great-grandchildren.) These guys were tough. Not only were they bad, they were heads and shoulders the baddest around. The gods had to make appointments to meet with them. So I was a little surprised when we started, and the wizard of the group (who had long since passed beyond the need to memorize those pesky spells) failed to collect the first clue to what was happening to their world. The clue was deep within a huge, black, underground lake within which swam gargantuan sightless monstrosities who had their own unholy city of basalt and bone. He was supposed to find the city, and discover the place where his apprentice had been attacked, and the object he had been killed for?but apparently I did WAY too good a job describing the scene and the most powerful wizard in the entire world turned and fled.
I always thought that was really funny?until it happened to me.
We had entered a town surrounded in a sickly yellowish fog. There was a stone wall around it and somehow our entrance had been lost. As we began to explore, we started having to make saving throws against?something. Once within the buildings of the town we discovered what, as half-dead townsfolk shambled out of their homes, eyes and tongues bulging from their faces with some unknown but obviously horrible disease. We turned tail and fled, the barrier of the stone wall lasting no longer than the casting time of a Move Earth spell. The next day the DM confided to me that the town had been the adventure he had spent hours and hours creating for us, and that what we had spent the rest of that night chasing was no more than a series of random encounters he had contrived on the spot.
I felt pretty bad about it, but I remebered my time in his seat, and I laughed. It was still funny.