Walt Disney World spans an enormous area, covering a ridiculous 25,000+ acres. Despite the presence of four theme parks, two water parks, more than 20 hotels and many other attractions, there's still plenty of free space for future expansion.

Not all of the unused space at Walt Disney World is part of wilderness preserves or untouched swampland, however. Some of it is occupied by attractions that have been introduced since the resort's debut in 1971 and subsequently shuttered and abandoned. Other areas are partially closed or undergoing renovation.

Let's take a look at 3 major areas of Walt Disney World that are no longer in use as originally intended.

3. Discovery Island

Located in Walt Disney World's Bay Lake, Discovery Island first opened to the public in April 1974 as Treasure Island. It was designed to be a wildlife observation attraction, and was renamed after being designated as a zoological park.

When the much larger Disney's Animal Kingdom opened in 1998, Disney opted to close Discovery Island. Many of the island's captive animals were moved to the new park.

While several alternative uses of the island have since been put forward - including turning it into an attraction based on Lost - it remains off-limits to guests. Urban explorer Shane Pérez reached the island in 2010, claiming to have discovered "abandoned buildings, cages, preserved snakes in jars, even old employee photos".

2. Disney's River Country

Back in 1976, Walt Disney World was short on attractions to keep guests on-site for more than a day or two. The only theme park at that stage was the Magic Kingdom, and EPCOT Center would not open until 1982. To add to its roster, the resort installed its first ever water park: Disney's River Country.

Located near Discovery Island on the shore of Bay Lake, River Country boasted a rustic "wilderness" theme. The theming was heavy on rocks and boulders, and was designed to resemble an "old-fashioned swimming hole".

The water that was used in River Country's slides and pools was drawn directly from Bay Lake, and passed through a unique filtering system. The natural feel of the park was enhanced by the sand that was abundant throughout.

When Michael Eisner took over as Disney CEO in 1984, he took a more competitive approach than his predecessors. He decided to build a full water park, Typhoon Lagoon, to take on nearby Wet 'n' Wild. River Country's capacity was limited, and its days were numbered. It shut on November 2, 2001, but remains in place today - it was abandoned rather than demolished.

You can see the current state of the park in this recent article.