While I've never been to a fully indoor small zoo, there's a small zoo in the North of England that I recently went to called the Lakeland Wildlife Oasis that is largely indoor, but has some outdoor enclosures too. Their indoor building has some fish tanks (including Lake Malawi Cichlids, blind cave fish, coral reef fish, axolotl and an African lungfish), a butterfly walkthrough with free-flying butterflies, a leafcutter ant colony and some tarantulas, and a Tropical Hall where all of the zoo's reptiles and amphibians are kept. The Tropical Hall includes a few species of poison dart frog, a panther chameleon, a black and white tegu, red-footed tortoises, and a Jamaica boa that shares its tank with Caribbean hermit crabs and Jamaica Anole lizards. There's also some potoroos and armadillos with their own enclosures, a nocturnal room with lesser tenrecs and Cairo spiny mice, and best of all, free-flying Javan sparrows and Rodrigues fruit bats, with a wire mesh on the ceiling for the bats to hang from.
I've been to a few entirely indoor zoos. Shedd Aquarium is my favorite zoo I've ever visited, and it's entirely indoors - though it's far from small! The best small all-indoor zoo I've visited in Jack Facente Serpentarium - a hidden gem specialist collection focusing on venomous snakes.
That zoo looks like it has a really nice charm to it! I love the evolution part, so clever and a nice educational way to start in a zoo.
