So I'm a pretty new DM, been running my first campaign for a few months now, and I may or may not have painted myself into a corner. My players are currently going to a maximum security underwater prison to break out one of the characters sisters. I've designed the layout of the prison and the way it works, and it's going to be a tough nut to crack. My players spent a lot of the last session trying to figure out plans to make it work, but don't really have any definitive ideas. I designed the prison from the point of view of making it maximum security. Something that could contain and hold the most dangerous of prisoners in a world where magic exists. I didn't design any 'loophole' that the characters are meant to exploit, deciding to leave it up to them to figure something out. Was this a bad idea? I'm starting to wonder if they are going to pull it off. Obviously I want them to succeed but I also want it to feel like they have figured out a way themselves, not had it handed to them by the DM. Do I need to have a failsafe built in where I have a way they can do it? Or should I let them struggle and possibly fail in a very significant side quest for one of my players?