The National Museum of Scotland looks like a fortress and to an extent it is. It has a perimeter wall protecting a higher central keep - a device to relate both to the high existing Royal Museum to one side on Chambers Street, and the lower buildings of Greyfriars on the other. It is clad in thick, beautifully-dressed blocks of glowing Scottish sandstone. Its great fat walls are punched with apertures, ranging from huge windows with heavy stone mullions to tiny arrow-slits and pinprick holes. It sits on the line of the old city wall. It has a cylindrical, freestanding bastion, set right on an important street intersection, that acts as the main entrance. The museum is made up of geometric, Corbusian forms, but also has numerous references to Scotland, such as brochs and castellated, defensive, architecture. Exposed red steel in the interior alludes to the nation's industrial heritage and the nearby Forth rail bridge, which can be seen from the museum's roof terrace.