Located in Pennsylvania’s Brandywine Valley, Longwood Gardens is home to 1,100 acres of formal landscapes, woodlands and meadows. A recent, 17-acre expansion offers day-trippers yet another reason to visit this gem founded more than a century ago by industrialist Pierre S. du Pont.

A centerpiece of the $250 million project is the West Conservatory, a new, 32,000-square-foot glasshouse designed by the New York firm Weiss/Manfredi. Noted for its asymmetrical, crystalline roof forms, the building appears to float on a pool of water.

“The structure’s pleated roof, branching columns and tapered perspectives extend the marriage of architecture and horticulture that is intrinsic to Longwood’s identity,” says principal architect Marion Weiss. Geothermal heating and cooling and a passive ventilation system that tempers fresh air are among the project’s sustainability initiatives.

Inside, an immersive Mediterranean Garden designed by New England-based Reed Hilderbrand invites visitors to walk among islands, pools, canals and fountains. Sixty species of plants, from agaves and aloes to cypress and bay laurel, flourish in the permanent installation.

“The West Conservatory’s Mediterranean Garden celebrates the particular beauty of species that thrive in that region’s dry climate,” says Kristin Frederickson, a principal of Reed Hilderbrand, “expanding understanding of one of our planet’s most diverse ecozones and its beauty, mutability and resilience.”