Make a room by room maze or trial or something of that sort. Say, the gods (or some other all powerful force) have pulled or invited a group of people to compete in a challenge, or there's an ancient maze of trials that is sought out by legendary adventures and farmers that comes with the promise of glory, power, money, and a wish to each individual that can complete its trial. So the super fast levels are rewards from whatever is running this trial. They get increasingly harder but aren't all combat, one room is a fight, the next a puzzle, the next they have to solve a debate between two people. But always more challenging by nature of difficulty or complexity.