Upon activation, the flagstones in a particular area reveal themselves to be the tops of huge stone pistons that begin pumping up and down randomly, slamming into the ceiling. There is a one-second delay between piston strikes, allowing characters to navigate between the madly firing stone pillars, if they are careful or lucky.
Dex, Saving Throws, or some sort of acrobatic skill (GM's decision), will allow the characters to get through unharmed. Anyone failing takes 3d10 HP damage from getting slammed into the ceiling.
Frederiksbjerg Skole (søjler) by RhinoMind under a Creative Commons Attribution-Share Alike 4.0 International License modified with Inkscape by David