I DMed a campaign for several first time players a while back. Early on, they were tasked with retrieving an item from a kobold den. They we expecting a video game style dungeon complete with treasure chests and clearly marked places to rest. They were expecting monsters who charged at them howling and fought to the death.

They got winding tunnels with choke points that were rigged to cave in and an organized defense focused on retreat and protecting the young. One of the players drew a map of the tunnels and even caught on to the fact that they were collapsed in an intentional order to delay them reaching the nursery chamber until it had been evacuated.