For more than 115 years, Longwood Gardens in Kennett Square, Pennsylvania, has been recognized as one of the world’s most important and beautiful collections of gardens and glasshouses. As he explores its indoor spaces, Karl Gercens, Longwood’s conservatory manager, covers historic features including the Orangery and East Conservatory and previews a history-making addition: the West Conservatory, which brings together 19th-century glasshouse traditions and the newest sustainable technologies.