Few flowers have as strong a grip on the popular imagination as the orchid. An obsession with orchid collecting has even inspired two popular books: Susan Orlean’s The Orchid Thief and Carol Goodman’s The Ghost Orchid. Though delicate in appearance, orchids thrive in environments all over the world.

But if you happen to live in, say, Pennsylvania, you won’t see many orchids on a typical neighborhood stroll (though they do grow in the wild). That’s why the newly restored Orchid House at Longwood Gardens is such a treasure. Inside, sophisticated control systems continually monitor temperature and light, making small adjustments throughout the day to keep all the plants happy. Thanks to a thoughtful, $5.5 million restoration led by John Milner Architects, hundreds of vibrantly colored plants bloom inside the concrete, glass, and steel structure.

Nestled in Pennsylvania’s Brandywine Valley, Longwood Gardens was established by industrialist Pierre S. du Pont in 1906 with the aim of conserving a nearby grove of trees, and it fully opened to the public in 1956. Now encompassing 1,100 acres of meadows, formal gardens, fountains, and woodlands, Longwood is one of the premier botanical gardens in the United States.

It was du Pont’s wife, Alice, who originally developed an interest in orchid collecting, according to Paul B. Redman, Longwood’s president and CEO. “Pierre and Alice du Pont were early founding members of the American Orchid Society, but it was really Alice who carried on the passion for orchids,” Redman says.

The du Ponts’ orchids came from the Caribbean, India, Thailand, the United Kingdom, Belgium, and France. A relative, Ethel du Pont, was an adventurous orchid connoisseur who traveled all over the world to find specimens, writing letters home to Pierre and Alice about them. Incredibly, among the orchids inside the restored Orchid House are about 60 plants from the family’s original collection.

The 1921 Orchid House at Longwood Gardens never looked like a typical Victorian Gothic greenhouse; it was built in a “stripped-down Neoclassical style,” according to Joshua Kiehl of John Milner Architects, who was the lead architect on the restoration. Kiehl and the rest of the team—which included contractor Bancroft Construction and several consultants and conservators—went to great lengths to preserve the structure’s form and style. They conserved much of the original bronze detailing, including window and door frames and display cases with delicate ironwork. They had a new glass roof built atop the existing steel roof frame and undertook painstaking analysis to repair and re-create the mosaic concrete that covers the building’s interior and exterior walls, floors, and columns. Yet much of what makes the Orchid House “work” is out of sight: a renovated system of underground tunnels houses utilities, such as a central steam plant that powers the heating system.