- This is a concrete slab, it seems well supported on pillars...
-- It's maybe not very stable.
--- I suppose that the weight of a human won't make any big difference.

--- We see nothing, it's very dark. We can hear an echo.

-- It seems a bit large for a bunker.

- It's excessively large you mean!

- Do you really see something?
--- I had forgot this detail...
- We talk about more than one hundred meters. This looks like a library.