Bunker Building Materials

[Timx0738]

Hello there

 

My roommate and I are somewhat amateur science nerds and like talking about weird things.

Our lastest fancy is if we were to go into the middle of the himalayas and find a mountain cave going about 0.5-1 km. into the ground and then build a bunker there.

 

Assume that the bunker could only be built using natural occurring materials without any means to improve them (ie. no alloys or chemical reactions, but smelting and refining is allowed).

 

What material would "score" the best for durability in relation to the effects of time and withstand the most chaos outside (shock, pressure, heat, cold ect.)?

If there could not be built any technology using electricity and the highest that could be achieved were clockwork what material used to build the gears and axles would "score" the best for durability in relation to the effects of time and withstand the most chaos outside (shock, pressure, heat, cold ect.)?

 

Thank you in advance for joining this brainstorm of ours :)