Different era theme. Medieval, renaissance, classical/roman.

Make them all the same to confuse people

Is this for Prison or OpPrison?

opprison, we are trying to make mines different and we need some clever ideas

Make sure the end portal is still in a mine

Make it so it looks like they could cave in on people when they are mining, so people pay attention, like parts that come down on the ceiling maybe... Or some fake bombs or cobwebs...