Deserts are fascinating regions characterized by extreme weather fluctuations and sparse precipitation. While hostile living conditions challenge ecosystems and societies, they allow mysteries to flourish.

Interestingly, a third of the world is classified as arid or semi-arid. Some of the largest deserts are the Sahara Desert, the Gobi Desert, the Syrian Desert, and the Great Basin Desert. That being said, deserts are made not only of sand dunes and rocky terrains, with Antarctica and the Arctic Desert being the largest cold deserts in the world.

Deserts challenge life… and science. Some mysterious megalithic structures and cities are believed to be evidence of extraterrestrial and divine existence.

Here are 15 strange desert finds scientists want to explain (but can't).

15 400 Mysterious Stone Formations Found In Saudi Arabia's Desert

The red deserts of Saudi Arabia hold secrets of ancient times and extraterrestrial signs. Thanks to Google Earth, though, scientists have recently discovered 400 stone structures that represent field gates. These beautiful structures - often referred to as the Gates to Hell - are a real archeological secret yet to be revealed.

14 The Nazca Lines Of Peru Are Still Perplexing

The Nazca lines located in the desert areas of Peru consist of more hundreds of geoglyphs and animal and plant designs. Interestingly, some of the lines run up to 30 miles and can be seen only from the air. The figures are massive and precise at the same time, making Nazca a subject of mystery.

13 Petra, The Pink City Of Mysteries

Hidden in the pink labyrinths of the Jordan desert, the ancient city of Petra is one of the most amazing places on Earth. Though social media channels are flooded with pictures of the impressive facade of the Treasury, the complex is still veiled in secrets. Scientists, for instance, can’t explain how the Nabateans managed to create Petra thousands of years ago.

12 The Discoveries In Uluru, Australia Shocked The World

Uluru is one of the most amazing places in Australia, sacred to many aboriginal people. It is situated in the so-called Red Center, famous for its desert landscapes and red rock domes. Rumors that an ancient city and a five-meter human skeleton were found there have been revealed to be false. Yet, Uluru and its spiritual importance are still mysterious.

11 The Secrets Of The Nabta Playa Area In Africa Are Standing Still

Located in the Nubian Desert, Nabta Playa is one of the most mysterious sites in the region. Nabta Playa consists of numerous tumuli, artifacts, and rock formations built more than 11,000 years ago. It was only a few decades ago when scientists discovered a megalithic stone circle there, perhaps the oldest astronomical alignment of stones in the world.

10 Were The Underground Churches In Ethiopia Built By Angels?

Do you believe in God’s existence? It’s assumed that the fascinating rock churches in Lalibela, Ethiopia were built by angels in one night. Officially, the churches are attributed to Kind Lalibela who wanted to create a New Jerusalem. Note that the Danakil Desert, not far from Lalibela, is one of the most dangerous places on Earth.

9 Believe It Or Not, You Can See Whales In The Sahara

It’s not a secret that the Sahara Desert is the largest hot desert in the world. Thus, you might be surprised that the Sahara Desert contains fossils of whales. Wadi Al-Hitan in Egypt is one of the most fascinating sites across the world that represent the evolution of the whales and their transition from land animals to sea creatures.

8 Gobekli Tepe, Turkey Can Rewrite History

The secrets hidden in Gobekli Tepe can help scientists rewrite history. Situated in the arid areas of Southeastern Turkey, the complex is a global mystery. Carbon dating estimates Gobekli Tepe to be over 12,000 years old… which predates human activity in the region by 6,000 years. Many believe that Gobekli Tepe proves that aliens did visit Earth.

RELATED: Gobekli Tepe: 15 Things About The Archaeological Site In Turkey (That Remain Unexplained)

7 Casa Grande In Arizona Is Still Veiled In Mystery

In the heart of the Sonoran Desert in North America, Casa Grande keeps ancient secrets, as per Atlas Obscura. Even though scientists know that the complex was made of adobe structures, nobody knows what the central building was for. The buildings were abandoned almost decades before Columbus’s voyage, so Casa Grande remains a secret.

6 The Stonehenge Of Gobi

The Gobi Desert is one of the largest deserts in Central Asia and the whole world. Note that Gobi is a cold desert; in Mongolian, "gobi" means "waterless place." This area is not only severe but mysterious. Hundreds of stone structures were found in Turpan, China; it’s believed that this Asian Stonehenge was used to worship the Sun.

RELATED: 15 Claims 'Ancient Aliens' Has Made About These Mysterious Landmarks (That Have Since Been Debunked)

5 A Gate To Another Dimension

Another secret left by the Nabateans is Mada'in Saleh, the second largest city after Petra. Situated between Petra and Mecca, just in the red center of Al Ula, Mada'in Saleh is attracting archeologists and travelers from all over the globe in the hope of revealing the secrets of the Nabatean kingdom, secrets hidden below the sand of the desert.

4 Vampires Are From Bulgaria, Not Romania

Aliens, gods, evil spirits; nobody knows the secrets of our world. What about vampires? Experts found vampire skeletons (each skeleton with a round stake emerging from the left side of the chest) in a couple of semi-arid sites in Bulgaria, including Perperikon – one of the most ancient rock structures across the globe.

3 Lost In The Maze Of Hemet, California

The Hemet Maze Stone, California is one of the fascinating petroglyphs in the US. It’s still a mystery who carved them and why. Interestingly, there are other mazes found in the Hemet area, including the Ramona Maze Stone, all on boulders ranging from four inches to several feet in diameter.

RELATED: The 10 Most Photogenic Deserts In The United States

2 Mars-Like Views And Rock Art In Wadi Rum, Jordan

From Mars-like views to challenging hiking trails, Wadi Rum, the Valley of the Moon, is one of the most beautiful deserts across the globe. The place amazes not only nature lovers, but archeologists. Thousands of petroglyphs and inscriptions tell stories about the Arabian Peninsula. It’s believed that some inscriptions indicate hidden springs.

1 Many Visit Them, But Few Understand Them

The mysteries of the Egyptian Pyramids fascinate scientists and alien believers alike. The construction of the pyramids in Giza, with all the hidden chambers and tunnels, is puzzling. Scientists still can’t comprehend how ancient Egyptians built these massive structures and aligned them perfectly. Were they helped by their Gods? Or extraterrestrials?

NEXT: 25 Pics Of Weird Things In The Desert (That Definitely Don’t Belong There)