I have a cage for a colossal sized creature that the pcs want to use a break action on. It's magically reinforced adamantine. It's also enchanted to drain strength of anyone who is in contact with the bars. They want to use part of an iron golem they destroyed as a sort of lever. One is a dragon disciple barbarian with like 30 strength hike raging. The other 2 will assist.
The bars are somewhere around 1 ft diameter thick or 6 inch radius.
They will effectively be using sunder to either destroy the bars, or strength to try to burst it.
Adamantine normally has a hardness of 20, but by magical reinforcement I'm assuming you mean the hardness has been enhanced (which would also increase the burst DC for the cage).
I can't find anything for cages specifically, but mithral manacles have a break dc of 30...so I would say adamantine should be at least that. Plus magical enhancements, and adamantine is stronger than mithral...So probably look at least a 40.
They wanted to use a lever to use a break action on the cage. But I think he gave up on that gonna just try to get threw its hardiness.
The bars are closer to 6" diameter not 12 so I told him the barbarian hacks at it he will eventually get threw it.