Da wikipedia:

* The château was built especially for the production, by art director William Hutchinson, it was 240 ft. wide and 50 ft. high, surrounded with 5,400 sq. yds. of heather, 400 ferns, 450 shrubs, 30 spruce trees and 6 weeping willows.

* Construction of the faux château proved too good. The script required its explosion, but it was so solid that 70 tons of explosives would have been required for the effect. Instead, a cork and plastic section was destroyed.
http://en.wikipedia.org/wiki/The_Dirty_Dozen