United States Botanic Garden Conservatory, Washington, DC

We have been to Washington, D.C. dozens of times over the years, but we had never visited the United States Botanic Garden until we lived for a year in Annapolis, Maryland working at the Maryland State Archives. It has now moved up to one of our top best places to visit. Here is a short description from the United States Botanic Garden website.

Constructed by the Architect of the Capitol in 1933, this historic Lord & Burnham greenhouse contains two courtyard gardens and 10 garden rooms under glass, totaling 28,944 square feet of growing space. 

Behind the scenes is a state-of-the-art completely automated environmental control system. Computers monitor the outside weather and automatically control misting, shade cloth, fans, air-handling equipment, heat and window vents to achieve a perfect range of day and night temperatures and humidity.

The plants are fabulous.