Disney World mysteriously closed an island 20 years ago and left it in ruins. Take a look inside.

Discovery Island is located in Bay Lake. Sam Howzit/Flickr/CC BY 2.0 Disney World once had a separate theme park on a private island called Discovery Island that was focused on birds and fauna. It closed in 1999.

Today, the abandoned park remains guarded and no one is allowed on. But a few people have snuck on to capture video of the decaying park.

The pictures and videos show a decrepit snack bar, a ruined animal hospital, and an eerily quiet loading dock. Disney World is marketed as a place of wonder, excitement, and magic. But, there's a secret side of Disney the company doesn't want you to see. On the official map of Disney World, there is a blank green mass in the middle of Bay Lake in Orlando, Florida. The mysterious island is not labeled and no one is allowed to enter - not Disney World guests and not even Disney World employees. But two decades ago this unlabeled island was actually another Disney amusement park called Discovery Island. It mysteriously closed in 1999. For nearly 20 years, Discovery Island has remained under lock and key, people banned from stepping foot inside. But a few years ago, YouTuber Matt Sonswa snuck onto the island to capture the park in ruins. This is what he saw.

Discovery Island originally opened in 1974 under its original name, Treasure Island. Bright Sun Films/ Getty The island was pirate-themed and was inspired by the Disney film "Treasure Island."

In 1976, the park was renamed Discovery Island and was meant to be a relaxing destination to view exotic birds and fauna. Bright Sun Films/ YouTube The park was marketed as an alternative for families who needed a break from the main Disney World attractions.

The park was known for its wide species of exotic birds that came from all over the world. Bright Sun Films/ YouTube The park's main attraction was its 150 birds.

From flamingos to cockatoos, the island was designed to be an avian paradise. Bright Sun Films/ YouTube You'd have to take a boat from the mainland to arrive at Discovery Island and experience the wild birds.

In 1999, Animal Kingdom opened, diminishing the number of guests at Discovery Island. Matt Sonswa/ YouTube Eventually, the birds were relocated to the new Animal Kingdom, leaving Discovery Island completely abandoned.

Today, the island lies in ruins, completely overrun by nature. The main loading dock, for example, where guests would disembark from boats and officially enter Discovery Island, still stands today. Matt Sonswa/ YouTube You can still see the small stand where someone would check your admission tickets in Sonswa's footage.

You can imagine the number of people who stood in this waiting area to board boats back to the main part of Disney World. Matt Sonswa/ YouTube Instead of being crowded with people, this boarding area is overrun with leaves and nature.

The first building you encounter is the Thirsty Perch, which was a concession stand at the entrance of the island. Matt Sonswa/ YouTube The Thirsty Perch was located in the hub of the island, making it a focal point for most visitors.

Some of the quirky decor on the Thirsty Perch still clings to the building's exterior. Matt Sonswa/ YouTube Some aspects of the island have withstood the force of nature and even hurricanes, according to Sonswa's video.

A small walk leads to one of the biggest buildings on the island, an animal hospital and nursery, which still stands decades later. Matt Sonswa/ YouTube The animal hospital also acted as the island's headquarters, making it the largest building on Discovery Island.

Inside the hospital is a cooler that still holds some medications and supplies for the animals. Matt Sonswa/ YouTube Sonswa has snuck his way onto the island a couple of times and each time he updates his viewers on the contents of this cooler.

Other parts of the building haven't remained as fully intact, however. Matt Sonswa/ YouTube With entire walls collapsing and nature growing inside buildings, it's easy to see how this island has been left uninhabited for decades.

Even the bathroom has become overrun by Mother Nature. Matt Sonswa/ YouTube Sonswa captured every corner of this island on camera to show the world what happened to the forgotten Discovery Island.

An incubator still stands in an otherwise empty room inside the hospital. Matt Sonswa/ YouTube Today at Disney's Animal Kingdom, the park's wellness center can perform veterinary services like surgical procedures, administer emergency medicine, and even help oversee pregnancies and births.

Near the animal hospital is a public restroom, which no longer has a roof, allowing for nature to take its toll. Bright Sun Films/ YouTube Today, there are 27 restrooms just in Disney World's Magic Kingdom ...

The island's main attraction was Avian Way, which guests entered through this door. Matt Sonswa/ YouTube Though now covered in overgrown fauna, this entrance brought you to the South American Aviary.

The doorway would lead to an elevated walkway which was covered in an overhead canopy. Bright Sun Films/ YouTube For the most part, the structural foundation of the walkway remains intact.

Some of the canopies also remain intact but most are weighed down with leaves. Matt Sonswa/ YouTube The Avian walkway was supposed to be a great way to witness the rare birds of Discovery Island.

In other parts of the island, trees have fallen onto the walkway, destroying the site entirely. Matt Sonswa/ YouTube Not everything fared well in the decades of abandonment.

It's difficult to imagine that this decrepit walkway was once filled with families on vacation. Matt Sonswa/ YouTube While poor attendance likely contributed to the island's downfall, Animal Kingdom saw 12.5 million people in 2017.

The island also has a service and maintenance area that was used by Disney's cast members. Matt Sonswa/ YouTube Although no one has worked at Discovery Island for decades, about 70,000 people work as Disney World cast members today.

On the ground, there is a pile of signs that were most likely taken down when the island was closing for good. Matt Sonswa/ YouTube The signs were originally used to help guests find their way around the 11-acre island.

Walking down the abandoned path is eerie, imagining the past employees who worked to keep this place running up until its demise. Matt Sonswa/ YouTube Now workers are employed to guard the island from intruders. In fact, Seph Lawless - another person who snuck on the island - said you're not supposed to get closer than 50 feet. "When you're on Bay Lake you're almost chaperoned," he told the BBC. "They have several security people on boats that watch you. If you get too close to the island they push you away. They'll yell at you, they're constantly watching you."

Even the ice machine still stands today. Matt Sonswa/ YouTube Lawless, the photographer who snuck on the island, is disappointed that the Disney company has not done anything with the island. "There was old attractions decaying, which was overgrown with weeds, trash scattered around," he told INSIDER. "I was shocked that a billion dollar company like the Disney Corporation would just leave part of their property like this. No billion dollar company should be powerful enough not to clean up their mess."

Other dilapidated structures can be found all over the island, like the cages that animals were once held in but now are covered in branches and leaves. Matt Sonswa/ YouTube The entire island is a mix of perfectly preserved remnants of the island's past and completely rotted structures that point to the park's untimely demise.