Yeah, whoever did this tunneled at least 20 yards, then had to get through three feet of steel-reinforced concrete, and that was before they got to the five inches of solid steel.
Bárki is fúrta át a 18 méter vastag betonszerkezetet, utána még át kellett fúrjon három méter vasbetont, és a végén még 10 centi acélt is.