Ran a 5e session where a bunch of 20th-level PCs were assaulting an abandoned prison. Two low-level monks were inside standing guard. The PCs devised a plan to quickly and quietly take the two out. They charged in and learned the two monks were bait. Over a dozen more monks stormed in, casting spells and fighting to the death. In the end, the result was never in doubt, but everyone had fun, and they were able to question a monk for details of wait was waiting deeper in the prison.