So my friends and I are all playing a campaign right now where we alternate DMs every session, so we can each throw in some of what we want into the mix. I'm designing a dungeon delve involving an ancient dwarven city full of automatons, sort of Skyrim style. I want to make the final 'encounter' in it more of a problem solving challenge than a fight, and could use some help designing it. I was thinking there would be a treasure vault at the end, but when the party opens it, or tries to, a failsafe activates that starts a self-destruct of the whole city. I want some sort of puzzle or similar to try and stop the explosion but I'm not sure on how, so I could use some input. Thanks in advance.