While some optical illusions have gone viral and stumped the internet, others you'll only see when you explore the outdoors.

From an underwater waterfall in the Indian Ocean to a surrealist scene in Namibia, we rounded up 12 naturally occurring illusions and optical phenomena that will make you do a double take.

Take a closer look below and find out how these illusions are created.

This may look like a surrealist painting, but it's actually a photo of Deadvlei in Namibia.

These are real trees.Anna Morgan/Shutterstock

Located inside Namib-Naukluft National Park, Deadvlei is a claypan dotted with many long-dead camel thorn trees, which have not yet decayed due to the area's dry climate.

The barren landscape, once flooded with water from the nearby Tsauchab River, is now a hot spot for photographers — many of whom have captured the contrast between the claypan's bleached white floor and sun-scorched trees.

Pictures like the one above are typically taken from a very low angle, so that the sand dunes in the distance, tinted orange by the sun, look like a painted backdrop.

This "underwater waterfall" is not what it seems.

There's a simple geographical explanation for this phenomenon.Myroslava Bozhko/Shutterstock

Along the shoreline of Mauritius, there appears to be a flowing river underneath the turquoise water of the Indian Ocean. While underwater waterfalls do exist, this isn't one of them. In this case, what looks like water is actually sand getting pushed off an underwater shelf called the Mascarene Plateau.

This salt flat in Bolivia is perfect for creating optical illusions.

No, this isn't Photoshopped.Kath Watson/Shutterstock

Bolivia's Salar de Uyuni, the world's largest salt flat, transforms into a giant reflective surface when it's covered in a thin layer of water, either from rain or nearby overflowing lakes. Stretching on for miles, completely level, the salt flat also appears to have an endless horizon, allowing photographers to create illusions by playing around with depth and perspective.

Yosemite's Horsetail Fall looks like it's on fire at a certain time of the year.

That's just water, not a flowing stream of lava.Dan Dunn/Shutterstock

Every year, around the second week of February, the setting sun hits Horsetail Fall in Yosemite National Park at a particular angle, illuminating the top of the waterfall. If the fall is flowing and the weather conditions are just right, the illuminated water glows bright orange and red, as if it's on fire.