Master architect I.M. Pei was one of the pioneers of modern underground architecture. His design for the Place Ville Marie in Montreal, Canada, incorporated an extensive underground shopping concourse under a high-rise office building and its surrounding plaza. The 1962 completion of this building planted the seed for the city's network of subterranean shops and walkways, a network that is now 20 miles long. Pei's next design with a significant underground component, the East Building of the National Gallery of Art in Washington, DC, marked his first use of glass pyramids to illuminate and enliven the underworld. Although other architects also use glass pyramids as skylights and roofs, the strategy became practically a Pei signature.

National Gallery of Art, East Wing Completed 1978

Pei's design for the National Gallery of Art addition relies heavily on triangles and trapezoids. The building includes an atrium gallery that is roofed with a glass-covered space frame (a three-dimensional array of sleek aluminum trusses). The underground component of the complex, which encompasses about one-third of the new space, consists of a below-grade level in the East Building and a broad concourse that extends westward under a street and a paved plaza to connect the addition to the original National Gallery building. More than simply a pedestrian corridor, the concourse houses casual dining facilities and a gift shop. Pei's first pyramids, a cluster of seven asymmetrical glass triangles, decorate the surface plaza and accent the concourse with daylight.

The Louvre Expansion Phases I and II completed 1989, 1993

The Louvre in Paris, France, was built, enlarged, and rebuilt almost constantly between 1546 and 1870. Originally a palace, it was converted to a public art museum in 1793 in the wake of the French Revolution. Ultimately, it stretched around three sides of a courtyard roughly the size of four and a half football fields placed side by side. Despite its enormous size, the museum was bursting at the seams with an art collection too vast to display. In addition, there was virtually no space to accommodate researchers and restorers, much less the 10,000 visitors who streamed through it each day. These practical concerns, perhaps seasoned with a pinch of ego, led newly inaugurated French President Francois Mitterrand to launch an expansion project in 1981.

A two-phase enlargement added 870,000 square feet of space to the Louvre beneath both the central courtyard and its extension past the original buildings. The French public readily accepted the fact that the new space would be out of sight. What they did not immediately embrace was the monumental skylight Pei proposed to crown the new subterranean reception area in the center of the courtyard. Wanting to admit plenty of light to the two-story underground addition and feeling that it was important to mark the museum's new entrance with a sufficiently impressive facade, Pei suggested topping it with a 71-foot-high glass pyramid whose base was 116 feet square. Although this structure would dwarf the people who approached it, it would rise only two-thirds as high as the historic Louvre buildings. Furthermore, it would be as transparent as possible, thanks to specially manufactured ultra-clear glass and a slender space frame design that stretched the limits of existing technology.

Besides expanding the underground space upward and allowing sunlight to pour through, the glass pyramid also provides views of the opulent old buildings that flank it. The pyramid's base is aligned with the existing buildings, but the 200-foot-square reception area underneath it is shifted so that its corners point toward the surrounding structures. Passageways from each corner carry visitors to various parts of the museum as well as underground shopping and parking facilities.

Each of the four passageways is flooded with light from a smaller glass pyramid. The 26-foot-square skylights topping the three paths to the museum buildings rise 16 feet above the courtyard. In the fourth direction lies a 270,000-square-foot underground commercial sector containing stores, restaurants, and four large auditoriums designed as venues for Paris' famous, haute-couture style shows. The skylight Pei designed for this sector is a 25-foot-tall, 37-foot-square, inverted pyramid that hangs from the ceiling and reaches nearly to the floor of the spacious commercial wing. A dramatic feature inside the underground space, this skylight is unnoticeable from the surface, where it is situated in a circular island in the middle of a divided road that crosses the courtyard's extension. The edges of the diamond-shaped glass panels that cover the upturned base of the pyramid are beveled to draw sunlight downward through the fixture. To keep the inside surface of the inverted pyramid free of dust and condensation, fans continually circulate filtered air through its interior. To prevent an errant vehicle from crashing through the skylight, its base is constructed of 1¼-inch-thick glass panels anchored in steel supports.

Rock and Roll Hall of Fame Completed 1995

For the Rock and Roll Hall of Fame and Museum in Cleveland, Ohio, Pei again designed underground space and a large glass pyramid, but with a very different relationship. The main exhibition hall and three theaters are hidden under a 50,000-square-foot concrete plaza that is used for outdoor concerts. Because the exhibits include many video displays and special lighting effects, the hall was designed as a windowless space where illumination could be completely controlled. So in this building, the glass pyramid does not function primarily as a skylight for subsurface areas.

Here, the glass structure encloses three-dimensional circulation spaces. Stairs and elevators carry people between the ground floor (with its lobby area, ticket counter, and museum store) and five higher levels that include some exhibits, a café, and access to exhibit and auditorium spaces inside the opaque portions of the building. What Pei calls a "glass tent" is more than a simple pyramid. Viewed from in front of the building, it looks a lot like the Louvre pyramid, although it is twice as tall. In addition, what is actually a glass parallelogram-shaped addition on one side creates the visual impression of a second pyramid recessed behind the main one. At the Louvre, the pyramid is transparent to allow minimal obstruction to the views of nearby buildings. In Cleveland, the pyramid is transparent to showcase the vibrant patterns of people moving around inside it. It leans against the rectangular tower that (along with other curved and planar, aluminum-covered concrete shapes) forms the rest of the building and provides a neutral background for the colorfully dressed tourists inside and for multicolored light shows that play across the structure's surfaces at night.

Miho Museum Completed 1997

From Kyoto, Japan, it takes nearly an hour to drive to the Miho Museum's site in a mountainous nature preserve in Shigaraki. Pei, a naturalized American who was born and raised in China, based his design on a folktale from his childhood. It told of a simple fisherman who entered a cave that took him through a mountain and out into a hidden valley where he discovered a lost paradise. Pei designed an approach to the Miho Museum that recreates this magical experience for each visitor.

Stopping one ridge shy of the Miho, visitors leave distractions behind as they walk away from cars or buses and, like the fabled fisherman, enter the mountain through a simple portal. The journey through the hillside begins with mystery: because the 650-foot-long shaft curves, the destination remains hidden from view. Lighting in the dulled stainless steel channel gradually becomes brighter, both heightening the anticipation of the journey and preparing the eyes for a return to sunlight.

Emergence from the pedestrian tunnel reveals a stunning vista with what appears to be a traditional tea house nestled among the trees. The view is framed by a tilted parabola rising above the path and separating a ring of suspension cables into an inviting triangular projection that draws the guest out onto a 400-foot-long footbridge. Crossing the deep ravine to reach the hidden paradise creates what Pei calls "a certain detachment from the world."

The visitor might catch a glimpse of one or two isolated rooftops tucked behind mounds of lush vegetation, but there is no hint that a 188,000-square-foot museum is tucked 6 feet under the hilltop. Only one-fifth of the structure is visible from the surface, and only small portions of that fraction can be seen from any single vantage point except an aircraft. This creates the illusion that there is only a scattering of small structures on the mountain.

Inside the museum, the illusion is transformed into a surprising sense of spaciousness. Though recessed into the earth, the structure overlooks the hills and valleys through a glass wall along much of its length. Individual galleries may feature controlled lighting to protect ancient artifacts, but passages between galleries bring visitors back into expanses awash with sunlight gently filtered through simulated bamboo slats under pitched, glass roofs. In some areas, like the entrance lobby, the simple roof is elevated in an irimoya style that tops a hipped roof section with a gable.. Pei fashioned this traditional Japanese form, often seen on Buddhist temples, from glass supported by airy space frames that soar as much as 45 feet skyward. The shape suggests a truncated square pyramid that is completed with an extended triangular section rather than a single point.

And what is Pei's point? Perhaps that there is an effective symbiosis between unimposing, underground spaces and sleek, crystalline structures that point to the sky.

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