It’s been more than 60 years since Philip Johnson had to traverse dense forest to reach the promontory where the Glass House now stands, in New Canaan, Connecticut. The architect immediately recognized the site’s enormous potential. Within an hour, he’d secured the 5-acre parcel, but it took three years and more than 75 conceptual drawings—vacillating from the monumentality of Claude-Nicolas Ledoux to the airiness of Ludwig Mies van der Rohe— before he built his defining Modernist home.

While the Glass House was conceived more as a work of art than as a residence, it did indeed serve as a home for its creator. When Johnson began spending weekends there in 1949, the glass-and-paintedsteel rectangle had already established his reputation as an architect of importance.

Over the decades, expanding the property to 47 acres, Johnson sculpted the landscape and filled it with structures that represent significant shifts in his architectural point of view. As one stands beside the Glass House and looks left to right, the Library/Study (1980), Ghost House (1984), Lincoln Kirstein Tower (1985) and Lake Pavilion (1962) express the Pritzker Prize–winning architect’s penchant for change. Using the land as a design laboratory, Johnson reshaped forests and hillsides, integrating them with the stone walls and structures. With no visual breaks to impede him, he relished his immersion in the falling snow or the light of the moon. Along the way, he added his art collection, a barometer of 20th-century art history. The whole Glass House estate, now a National Trust for Historic Preservation Site, opened to the public on June 23rd for the first time in more than 50 years.

The Glass House’s 1,728-square-foot interior is a spare, elegant arrangement of low walnut cabinets and Mies van der Rohe furniture. Mostly brought from Johnson’s New York apartment, these pieces are an acknowledgement of the inspiration Johnson found in his mentor’s glass-box design for the Farnsworth House in Illinois. Other prominent features are an 82-inch, papiermâché- over-plaster maquette of Elie Nadelman’s 1930 “Two Circus Women,” which was rendered in Carrara marble for the New York State Theater at Lincoln Center, and a Baroque landscape painting attributed to Nicolas Poussin. “Burial of Phocion” (1648–49) related to the surrounding scenery and was selected for the Glass House by Johnson’s close friend Alfred H. Barr Jr., the first director of the Museum of Modern Art. A cylindrical brick bathroom is the only floor-to-ceiling object in the 56-by-32-foot house. The same red brick is on the floor and each of the four quarter-inch glass facades is bisected by a door. “These structures are architectural treasures of a movement whose significance is not yet fully realized,” says Jack Pyburn, chair of the American Institute of Architects Historic Resources Committee. “The scope of their importance and value to architectural history will increase with time and reflection.”

On the same promontory from which the Glass House faces the setting sun, the adjacent Brick House, also completed in 1949, marks the opposite side of a connecting courtyard. The Brick House’s solid facing wall preserves privacy but is more significant as a counterpoint to the Glass House’s transparency. Used for guests and as the center for the estate’s utilities, its interior was renovated in 1953 to reflect Johnson’s break with pure Modernism. The bright, skylit hallway is hung with selections from Brice Marden’s 1986 “Etchings to Rexroth Portfolio.” The bedroom where Andy Warhol occasionally slept has billowy white vaults curving overhead, walls and round windows draped in Fortuny silk, and above the bed is “Clouds of Magellan,” a 1953 bronze-and-steel sculpture by Ibram Lassaw. It was here that Johnson napped and relaxed in the chocolate-brown reading room stocked with his books on history and philosophy.

As founding director of MoMA’s Architecture and Design department, Johnson had more than ample opportunity to explore au courant art, but meeting David Whitney in 1960 changed his aesthetic and personal life forever. Whitney, then a student at the Rhode Island School of Design, approached Johnson after hearing him lecture at nearby Brown University. Their conversation about the Glass House led to an invitation for Whitney, which began an intimate 45-year partnership steeped in love of art and architecture. “Philip always said, ‘David has an eye for art,” recalls Hilary Lewis, the site’s Philip Johnson scholar, who collaborated with the architect for a dozen years on book projects.