A few particularly nature oriented highlights:
- Saturday at 8:30, a bike tour of the Anacostia River
- Saturday and Sunday at 10:00 and 1:00, a tree tour on Massachusetts Ave
- Saturday at 10:00, Discover the National Arboretum
- Saturday at 10:30, a tour of the National Garden at the US Botanic Garden
All tours are free, but most require advance registration. Much more info at Cultural Tourism DC's WalkingTown DC page, or just download the PDF brochure for the full schedule.
As always, there's much more on our full calendar.