John G. Shedd Aquarium 

Home to over 32,500 animals including fish, marine mammals, birds, snakes, amphibians, and insects, the Shedd Aquarium is one of Chicago's finest museums and research centers. Visited by over 2 million people every year, the aquarium features the Abbott Oceanarium, the largest indoor marine mammal facility in the world where visitors can get up close and personal with beluga whales, dolphins, and penguins (just to name a few!). 

The aquarium exhibits were first opened to the public in 1930, and at the time it was the largest indoor aquarium in the world, and the first inland aquarium with a permanent saltwater fish exhibit.