My shoes are getting ruined at Philip Johnson’s Glass House. It’s raining hard, and by wandering off the property’s gravel paths and onto its lush grass, I’m giving them a good soaking. But as I follow Executive Director Gregory Sages into the recently restored Sculpture Gallery, my concerns about my footwear fall away.

I’m suddenly inside a piece of origami, with white walls folding in and out around and below me. Overhead, a massive skylight forms the building’s entire roof, bringing in soft gray light and framing views of tree and sky between thin steel tubes. Because Sages is accompanying me, I’m permitted past the main entry level and down the brick stairs, which have no railings and are off-limits to visitors.

As we descend through the 3,650-square-foot gallery’s five staggered levels, the space keeps changing on me—one minute it’s expansive, the next it’s intimate. This is not a building for sitting still. Which makes sense; its architect and former owner, Philip Johnson, told a National Trust interviewer in 1991 that he sat down “very, very rarely.”

The Sculpture Gallery is part of Johnson’s 49-acre estate in New Canaan, Connecticut, a National Trust Historic Site since 2007. Thousands of visitors per year flock there to see the Glass House itself, a tiny, transparent sensation unveiled by Johnson in 1949. He beat his sometimes-friend and always-competitor Ludwig Mies van der Rohe by two years: Mies completed the equally iconic, all-glass Farnsworth House—also a National Trust Historic Site—in 1951, annoyed that Johnson had admittedly borrowed his idea.

Without the Ohio-born Johnson, Modernist architecture might never have taken off in the United States. He and collaborator Henry-Russell Hitchcock created a groundbreaking 1932 show at the Museum of Modern Art called Modern Architecture: International Exhibition that introduced the American public to the unadorned work of architects such as Mies, Walter Gropius, and Le Corbusier. The exhibition kick-started Modernism as the dominant American architectural style for the next half-century.

Over that same period, Johnson became a consummate connector of influential people, especially in New York society circles. He helped convince heiress Phyllis Lambert to hire Mies to design the Seagram Building in New York (1958), an instant classic. Along with serving as an associate on the project, Johnson designed the building’s legendary Four Seasons restaurant, holding court from his corner table there for the next several decades. (In a major loss for preservation, the landmarked restaurant space was disassembled last summer, and its contents, including furniture by Johnson, Mies, and Eero Saarinen, were auctioned off.)

The most coveted seat of all, though, was in the living room at the Glass House, about 45 miles north of the city, where cultural heavyweights such as Frank Lloyd Wright, John Cage, and Andy Warhol would gather to discuss the issues of the day. Architecture critic Vincent Scully called the Glass House “the longest-running salon in the history of the United States.”

In 1960 Johnson met David Whitney, who would become his life partner until both of their deaths in 2005, six months apart. As he developed his career as an art curator, Whitney helped Johnson cultivate his already strong interest in contemporary art, and the pair eventually amassed an impressive array of work by luminaries such as Robert Rauschenberg and Jasper Johns, often before the artists were well known.

The Glass House has few places to display art; the walls are meant to bring in unbroken views of the meticulously landscaped natural surroundings. “The windows are like paintings,” says the site’s curator and collections manager, Irene Shum. Johnson had already designed a more private building for the property, the Brick House, and the Pavilion, a little folly on the estate’s manmade pond. He decided to create a separate space where he and Whitney could keep their growing collection, dubbing it the Painting Gallery. The mostly underground building opened in 1965, and its large moving panels allowed Johnson and Whitney to conserve and display the artworks they acquired over the years in a relatively small, climate-controlled environment.

They also placed their burgeoning collection of Modernist sculpture there, but found that the moving panels, so perfect for holding paintings, didn’t work as well with three-dimensional objects in the room. “Every time I took a great big panel and moved it around the rack to see the next painting, it would bang into a very large piece of sculpture,” Johnson said in his 1991 interview. He seized on the problem as an opportunity to design another building, which seems to have been a regular occurrence; by the time of his death, the rolling hills of the Glass House estate contained 14 structures. (Two were pre-existing, but Johnson designed the rest.)

With the design of the Sculpture Gallery (1970), Johnson wanted to create a space where each sculpture could be isolated against a plain background, without any other artwork within a viewer’s line of sight. “I wanted a way, a proper way, to look at sculpture,” he said. So he nestled the building into a slope on the north side of the property, within view of the Glass House’s bedroom. It has no windows to bring in distracting vistas from outside—instead, an enormous skylight made of structural steel and glass keeps the entire space naturally lit, and cold-cathode lighting tubes provide extra illumination. On sunny days, hundreds of bold shadow lines crisscross the bright white walls, creating a pleasing sense of disorientation.

About those wide brick stairways with no railings: Johnson had a penchant for introducing elements of slight danger into the work he did for himself and Whitney. “I like going down these steps,” he said in the 1996 documentary Diary of an Eccentric Architect. “I have to pay attention where I’m going not to pitch over. It gives me a new way of looking at each sculpture.”

Architect Dennis Wedlick worked for Johnson in the 1980s and early ’90s, during and after college. He remembers the couple treating the Sculpture Gallery like another room in their house, living comfortably with their museum-quality works by art-world stars such as Bruce Nauman and John Chamberlain.

“When I first walked through it, what I noticed is, it doesn’t feel like a museum,” Wedlick says. “You are casually walking down into a space and come upon things. Even work that is very, very provocative seems approachable in that space. [Johnson and Whitney] being in there was just a routine thing. They never, ever gave you the impression that you were in anything but a house.” The couple would set up bars there during parties, and Johnson often worked in the space—at least, he did before he got the itch to design another building, a little library/study completed in 1980.

By the time Johnson and Whitney died and left the Glass House estate to the National Trust, the Sculpture Gallery was ready for a restoration. The 12 sculptures in the space were in good condition, and so was the building structure. But rust covered the tubular steel skeleton along the ceiling, and the lights and heating system had stopped working. The single-pane glass in the skylight had started to leak, and the gutters were constantly clogged or overflowing. Paint was wearing off the exterior walls.

The Glass House and the Painting Gallery needed attention more urgently, so the National Trust and the Glass House staff focused on those buildings first. But the idea of restoring the Sculpture Gallery was always on the table. Alan Ritchie, who worked with Johnson for 27 years and still runs his successor firm, Philip Johnson Alan Ritchie Architects, did a feasibility study in 2012 and 2013 with his business partner, Marko Dasigenis. The biggest issue, they found, would be replacing the glass roof. Hundreds of differently sized glass pieces would have to be custom made, and updating the skylight with today’s energy-efficient double-pane glass while maintaining the look of the original would be difficult—and expensive.

Luckily, a solution presented itself in the form of Ted Hathaway, chief executive of Oldcastle BuildingEnvelope®. The company supplies custom-manufactured glass, skylights, and other products for buildings designed by high-profile architecture firms such as Gensler and Foster + Partners, and Hathaway wanted to help the Glass House. He offered Oldcastle BuildingEnvelope’s services in custom engineering and producing replacement glass for the skylight, a donation worth about $275,000. “We [did] this because we’re part of the architectural community and we’re committed to the preservation of design,” Hathaway says. This contribution served as a catalyst for the $2 million restoration project, the largest one ever undertaken at the Glass House.

Work began in March of 2015, with the delicate task of boxing up and moving the sculptures. Two were moved to Da Monsta, a curvy 1995 entry pavilion on the property. Three works were lent to the traveling exhibition Frank Stella: A Retrospective, organized by the Whitney Museum of American Art and the Modern Art Museum of Fort Worth, and the remaining seven were protected in place, sealed tight in structural wooden crates. Then the construction team, led by Andrew Wilson of Nicholson & Galloway, built a watertight work platform inside the building, under the roof. It covered the entire area of the gallery, so the crew would be able to replace the skylight and restore the cold-cathode lighting system without disturbing the crated sculptures below. They called it “the dance floor.”

Oldcastle BuildingEnvelope painstakingly re-created each piece of glass in the exact dimensions and color tint of the original. Although the new glass is double-pane, glass technology has come such a long way that the extra layer is almost invisible. “You can’t tell at all, not even from the side,” says Brendan Tobin, the Glass House’s senior buildings and grounds manager. And the new glass’ UV filter, which wasn’t available in 1970, helps control heat gain in the un-air-conditioned space.

Then there was the exterior paint. Johnson and his contractor, Louis Lee, had decided to paint the brick Sculpture Gallery white at the last minute, to the chagrin of the skilled Italian stonemasons who had smoothed the mortar joints to perfection. “The masons were flabbergasted,” recalls Horst Hahn, who served as Johnson’s project architect at the time.

Johnson and Lee concocted a mix of paint and cement, creating a rough texture that showed every brushstroke. Ritchie, the lead architect for the restoration, and executive director Sages spent weeks testing different combinations to make sure they could reproduce the original. “People think that white is white, but there are thousands of whites,” Ritchie says. After brushing all the existing paint from the exterior brick, Wilson’s crew applied the approved mixture.

They also replaced the building’s failing gutters and threaded them with heating lines to prevent freezing during snowy Connecticut winters. Phase two of the restoration, which will take place sometime this year, will entail replacing the footing drains and waterproofing the Sculpture Gallery’s foundation to protect against moisture infiltration.

The dance floor is gone now, and the new skylight is in. On my visit, the crisp white building nestles into the glistening green lawn, just as it does in photographs from the 1970s. Ozymandias, a cast bronze Julian Schnabel sculpture of a tree lying on its side, stands guard outside the gallery. “This is a piece I’m very fond of,” said Johnson in Diary of an Eccentric Architect, patting it affectionately.