What can penetrate 6ft thick rebarred concrete?
A bulldozer or wrecking ball could go through it with some effort, but not much other than those. But have you thought about how heavy the structure will be and what type of foundation system will be needed? Also, concrete has zero insulation value so beyond the cost of all this concrete, you will need to either remote wall the insulation (foam panels) or build a secondary wall for insulation. And you better plan all the doors and windows carefully because it would extremely difficult if not virtually impossible to make any changes later on.
cosmic rays will go right through , neutrons,neutrinos, all sorts of stuff.