As humans, we built a Great Wall. We built some pyramids. We also built a lighthouse and a temple and some hanging gardens.
...but we can't just build an underwater river. It's time to make way for Mother Nature's craftsmanship on your list of must-see world wonders.
1. Pink lakes
A breed of tiny algae called Dunaliella salina is usually to blame for turning various lakes around the world into milky, Pepto Bismol-y shades of rose. You can boat, swim, and splash in pink lakes from Australia to Africa.
2. UFO clouds
They're actually called lenticular clouds, and they often form around mountains when warm, wet air meets non-turbulent winds. Catch them around Mt. Rainier in Washington or Mt. Hood in Oregon.
3. Mud volcanoes
They'll never grow to the size of regular volcanos, but they've been held responsible for deaths just the same. Mud volcanos erupt when "pockets of underground gas force their way to the surface." Most of them are in Azerbaijan.
4. Blue lava
When pure sulfur burns at night, it glows neon blue. See for yourself -- but don't get too close! -- at Kawah Ijen Volcano in Indonesia. 
5. Moonbows
They're like rainbows, only they happen when moonlight passes through a thin spray of water. Look for them near waterfalls or in Hawaiian lava fields.
6. Salt flats
If lake or pond water evaporates instead of seeping into the ground, it'll leave mineral compounds behind on the surface. Such is the case at Bolivia's Salar de Uyuni salt flat and the Bonneville Salt Flats in Utah.
7. An underwater river
Something about hydrogen sulfate makes this stream of saltwater heavier than the water around it, so it flows just like an above-ground river. Scuba divers love to explore this wonder near the Yucatan Peninsula in Mexico. 
8. Bioluminescent blooms
When groups of light-producing plankton drift to shore on the same tide, their enzymes make it look like an underwater black light party. You'll find them in the Maldives, among other places.
9. The Northern Lights
Earth's famous light show occurs when particles from our atmosphere collide with particles from the Sun's. You'll see them best near the North Pole in countries like Canada, Greenland, Iceland and Norway, but they're also visible from some U.S. states like Michigan.
10. Brinicles
When really salty water leaks out of sea ice (because sea ice is apparently a thing), it gathers into what looks like an underwater icicle. Brinicles are common in the ocean near Antarctica-- and people go there to swim with them.
11. A multi-spouted geyser
In the 60s, well drilling caused minerals to break out of the ground and pile up in the deserts of Nevada. The glob-like result, known as Fly Geyser, is coated in colorful thermophilic algae. You can peek at it, but stay behind the fence-- this ranch is private property. Its owners, however, might agree to give you a seasonal tour.
12. The Grand Prismatic Spring
There are other hot springs in the world, but none as technicolored as this one in Yellowstone National Park. The rainbow tone comes from bacteria that live on the edge of the spring. 
13. Penitentes
These blades of snow and ice can grow to 16 feet high. We think they might be on Jupiter's moon, but you can also see them on Earth, in a special region of the Andes Mountains.
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