From the DAM website:
In 1971, the museum opened what is now known as the North Building, designed by Italian architect Gio Ponti and Denver-based James Sudler Associates. The seven-story structure, 210,000-square-foot building allowed the museum to display its collections under one roof for the first time. This architectural icon remains the only completed project in the United States by this important Italian master of modern design.
The North Building was an innovative move away from traditional, temple-style museum architecture. More than a million reflective glass tiles on the building's exterior complement the dramatic windows and pierced roofline of the building's castle-like facade. "Art is a treasure, and these thin but jealous walls defend it," said Gio Ponti.