US National Arboretum

While the National Capitol Columns are what drew me in, the visitors center is a interesting mid-century modernist building designed by Deigert & Yerkes. Currently under renovation, it should be back in tip top shape in a few months.

If you're a into gardens, plants, or landscape architecture I recommend you spending some time at the arboretum. Here's a few more photos of the columns.

Cooper approved.