It was the fourth park built there , and it opened on April 22 , 1998 . It is the largest Disney theme park in the world , covering more than 500 a. It is also the first Disney theme park to be themed around animal conservation , a philosophy once pioneered by Walt Disney himself . The fourth park built at the resort , it opened on April 22 , 1998 , and it is the largest single Disney theme park in the world , covering more than 500 a. It is also the first Disney theme park to be themed entirely around animal conservation , a philosophy once pioneered by Walt Disney himself .