On a whim we popped into the Botanical Garden in Washington DC. We are strolling past the Capitol Building and wandered in. It’s free admission, and not huge so it was a fun 30min detour.
Some of the areas were closed when we were there, I think they were refurbishing bits. Inside the Conservatory there are different areas for the different climates, like the tropics, desert, and Mediterranean. There is also a section for medicinal plants, endangered plants, and a primeval garden recreating the Jurassic era (complete with little dinosaurs).