Abstract: A building structure having high blast and penetration resistance, including a plurality of walls at least one of which is of a sandwich construction including four composite panel structures each including a first group of face panels having interlocking ends, a second group of face panels having interlocking ends spaced from said first group, a plurality of laceing panels extending diagonally between the two groups of face panels and having ends interlocking with the interlocking ends of the two groups of face panels, and a filling material filling the spaces between the two groups of face panels and embedding the laceing panels. The filling material filling the spaces between the face panels is a solid material such as cast concrete, and the space between the composite panel structures is filled with a loose filling material, such as loose sand, gravel, pebbles or stones.