Almost hidden in the lower south end of the zoo is one of its multi-purpose structures called Amazonia. Within you'll discover a multistory rain forest. The bottom level gives you access to huge aquariums filled with enormous and beautiful fish and even turtles. When you reach the floor above, these tanks form the surface of the "River" that flows through the multi-story jungle. Now you can look over the edge and down upon the same gentle giants you'd just been watching glide around at eye-level.
The jungle is also a free-fly Aviary; however on this visit there were only 5 birds present. A beautiful Roseate Spoonbill (who is always there), and a quartet of Scarlet Ibis. Sometimes there have been Bolivian Titi Monkeys, at other times a Three-toed Sloth. When mammals are present, there is also a keeper to make sure nothing harmful can happen. Even when they are there, things can go awry. I was there one time when the sloth slipped and fell out of a tree to the shock and alarm of everyone.
When I first arrived in the lower level there is a pool with River Rays in it. Sometimes there are also ducks and usually the Roseate Spoonbill. When I didn't see any birds I leaned in and looked up to discover the Roseate Spoonbill looking back down at me. I took a couple of pictures, and with no one else around, I also spoke to her. Low. Gently. When I got to the end of the jungle pathway as I was looking down at the fish in the river there was a sudden "wooosh~ FLOP!" And there she was, perched on the railing practically arm's length away. She proceeded to watch me as I took more pics.
After leaving this area, you enter a lobby that takes you to an Amphibian Lab full of displays and views through large glass windows into areas where Amphibians are studied and bred. Theoretically, you could end up there when a keeper or a scientist was actually working; however, in maybe 15 visits--I've never encountered this. In general, you never see volunteers at the National Zoo, and keepers are likewise few and far between. The amphibians are dominated by various species of Poison Dart Frogs, but there are other frogs, newts, salamanders and a most curious creature called an Aquatic Caecilian. At one point, I met this lovely young woman who was more than happy to chat about PD Frogs. When we ended our conversation, I wished her a "wonderful visit."

The facade is really lovely; an homage to late 20th century post-modernism. Jungle to right and amphibians to the left.
The first thing you see is this pool of Amazon River Rays
Spotted Amazon River Rays, there are three members of the Potamotrygon species: P. castexi, P. Leopoldi, and P. Motoro. As I stood by the edge, they came to me--such curious and beautiful creatures. Unfortunately, I had nothing to feed them.
Looking up to the upper level I discovered the Roseate Spoonbill, Platalea ajaja.
In the under corridor massive glass windows display the animals swimming in the "River."
Up a floor and you are on a pathway through a rain forest.
The quartet of Scarlet Ibis, Eudocimus ruber.
Across the lobby and down the stairs into the Amphibian Center.
African Clawed Frog
Xenopus laevis
Two species of Poison Dart (PD) Frogs
Blue PD Frog
Dendrobates tinctorius azureus
Dyeing PD Frog
Dendrobates tinctorius
Bumblebee PD Frog
Dendrobates leucomelas
A pair of Eastern Red Spotted Newt.
Eastern Red Spotted Newt
Notophthalmus viridenscens
Green and Black PD Frog
Dendrobates auratus
The next two PD Frogs are species I have never seen before in a North American zoo.
Blessed PD Frog
Ranitomeya benedicta
Brazilian PD Frog
Ranitomeya vanzolinii
Looks like they are playing a game of PD Frog "Twister".
Gray Tree Frog
Hyla versicolor