Another Pennsylvania entry on our list, Longwood Gardens, near Philadelphia, boasts one of the great historic conservatories in the United States. The conservatory is home to 20 separate garden areas, which contain more than 5,000 different species of plants. The conservatory consists of three greenhouse complexes that provide 4.5 acres of indoor growing space.
It would take two hours to stroll through all the gardens if you kept a leisurely pace and didn't stop. People who want to truly appreciate the plant life at Longwood can easily spend a day exploring. This is truly a conservatory in a classic sense, with arching glass roofs, marble floors and ornate fountains and ponds.