I had an idea for a puzzle for my lotfp;wfr campaign. A big one, which would take up a lot of a session to figure out, and could easily make the advendure shit if I botched it.
There's a room full of seemingly normal items. A vase full of flowers, a painting on the wall, a grandfather clock etc. In the middle of the room is a portal, leading to a never ending battle.
The goal is to find a magic sword, or some other important item, and the players know that the item is being used by someone on that battlefield. The item has to be desirable enough that the players are willing to wade through a lot of crap to get it.
Finding this one item in a sea of people trying to kill each other is next to impossible, so if the players just decide to wade into the mass of sweaty men and sharp edges, it should be immediately made clear that they're unlikely to find anything before they get killed.
However, the PCs can influence the battle by interracting with the objects in the portal room. Each object has it's own bizarre function, turning the painting sideways, for example, makes the entire battleground turn sideways, and fiddling with the clock affects time in the battle. Picking a dead flower kills off every last soldier, (except the PCs, if any of them should be on the other side of the portal) while picking a fresh one wakes them up again. The fruit bowl stops the fighting and makes the warring factions start feasting to celebrate their newfound friendship.
The players should know a little bit about the battle before encountering the puzzle. Maybe it's a magical reenactment of a historic siege or something. This way they can combine their knowledge with the tools at hand to try and create favorable conditions for exploring particular areas. Or they could have some idea about who owns the item in question, and be able to deduce where that person might be based on what happens.
"Look, someone cut off the trebuchets counterweight. Everyone knows Durgon the Shadow was one of the imperial army's most devious saboteurs. Stop time so we can go investigate."
"But that's beyond the castle walls. We can't climb them, and the gates won't open if we stop the clock."
"Then turn the painting left, I'll walk up the wall, and then down the other side once you turn it right."
I'll have to go over this a few times before using it, but I hope it can provide a nice incentive for the players to let loose and be creative. My biggest worry is that they'll find some easy way to blow through it quickly. I'd hate to have them finish it in fifteen minutes because I overlooked some detail or combination of elements that solves the problem for them.
The way I'm constructing the event is to provide the tools at the PCs disposal, and clearly determine what they do and how they interract if used together. Then I'll draw a map of the battlefield and a rough step by step account of how the battle will go when not meddled with. Then the players can ravage it at their own pleasure.