The World of the Future Fair was a futuristic theme park located in Gotham City.
During its initial days, the Fair was an amusement park very visited by the population of Gotham City. Bruce Wayne visited the park along with his girlfriend Andrea Beaumont. They really enjoyed the experience, and in the park, Bruce watched a futuristic car that would serve him as inspiration for the Batmobile.
Long after it closed down and became derelict, the Joker used this theme park as his hideout. Salvatore Valestra visited this park to ask for help from the Joker, but he instead killed him with his toxin and dynamited his penthouse. Later, the Phantasm visited the Joker to kill him. Batman foiled the attempt, but the Fair exploded because Joker had rigged the complex. All three survived the destruction.
The World of the Future Fair was mainly inspired by the 1964 New York World's Fair. Furthermore, the song "Welcome to the Future" is similar to "There's a Great Big Beautiful Tomorrow", the song played in the Disney/General Electric sponsored "Progressland". On the other hand, the rocket and planet centerpiece was inspired by New York's famous Trylon and Perisphere exhibit from the 1939 New York World's Fair.