[marktwain]

with some of them being 10km below the survace and impervious to bomb strikes.

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I doubt any are 10km below the surface. The engineering problems of creating such a tunnel are immense. Simply surviving the heat at such depth is a very tough problem. The temperature underground increases at about 75 degrees F for each km. At 10 km it would be about 750 degrees above zero.

[marktwain]

with some of them being 10km below the survace and impervious to bomb strikes.

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I doubt any are 10km below the surface. The engineering problems of creating such a tunnel are immense. Simply surviving the heat at such depth is a very tough problem. The temperature underground increases at about 75 degrees F for each km. At 10 km it would be about 750 degrees above zero.

[HartleyMBaldwin]

I doubt any are 10km below the surface.

They're not. The Mponeng mine in South Africa is the deepest mine in the world, and it hasn't reached 4 km depth yet, though it's planned to around 4.2 km.