VARach, Washington DC, Columbia
Don't miss this charming center! They've packed an enormous amount of fauna and flora into the acreage and it's well worth a visit and the minor cost of entry. It's really well designed and also includes a small garden where they grown local plants, a superb butterfly house, and a space where you can learn about local culture.
You can wander on your own but spring the extra few dollars for a guide. I can't remember our guide's name unfortunately, but he was excellent. It's an interesting tour (not too long but long enough) and he pointed out plants and animals that we would have definitely missed (eg cool orange toed frog *under* a leaf by the pond). By the end of the tour we had a family and 2 couples lurking in the background because it was so clear we were getting so much from the guide.
As a note - we really wanted to see sloths but they had moved to the edge of the center boundaries to graze and so the guide took us (and all hanger-oners :) to the area near the parking lot out on the access road -after the tour was finished and on his own time- to help us find the one that was rumored out there. We found not one but three and the guide spent a other 20+ mins hanging around there with us teaching is about the sloths and sharing his telescope with us. Really great guy.
The center is well worth a stop-by in between zip lining and hot springs! Don't overlook!