Fairy Chimneys, Turkey
These strange conical spires are found in the Cappadocia region of Turkey.
Several million years ago, active volcanoes spewed volcanic ash that covered the ground. Rainwater and wind eroded the soft compressed volcanic ash, leaving behind the harder overlying basalts, forming the fairy chimneys.
Ha Long Bay, Vietnam
This spectacular landscape is dotted with limestone pillars, arches and caves. The rocks have been shaped by the repeated rise and fall of the sea over 500 million years. The bay also includes over 1600 islands and islets, most of them uninhabited.
According to legends, dragons created the islands and rocks to keep invaders out of Vietnam.
Eye of the Sahara, Mauritania
Formally known as the Richat Structure, the Eye of the Sahara looks like a bullseye from above.
Located in the Sahara desert, it is a dome-shaped rock structure about 50 km across. Once thought to have been caused by a meteorite impact, it is now believed to have formed from uplifted rock that was later eroded.
The Great Blue Hole, Belize
This underwater sinkhole is 320 m wide and 125 m deep, and a major scuba diving attraction. It is part of the Belize Barrier Reef, which is in turn part of the Mesoamerican Reef.
This hole is believed to have formed during the recent ice ages, when a submerged limestone cave system collapsed due to changes in the sea level. Huge stalactites and stalagmites are found in the hole, which contain records of past climates.
Moeraki Boulders, New Zealand
Resembling giant turtle shells, these spherical boulders lie strewn on New Zealand's Koekohe Beach.
These boulders started forming in sediments on the sea floor over 60 million years ago. Carbonates built up around a central core, similar to the way pearls form around a speck of grit.
According to Maori legends, the boulders are remnants of gourds and eel baskets, washed ashore from the wreck of a sailing canoe.
Zhangye Danxia, China
These rainbow mountains look like something out of a painting. The Danxia landforms, found in China's Gansu Province, are made of strips of red sandstone that were deposited over millions of years, like slices of a layered cake.
But a word of caution: many online pictures of these hills are probably the result of image manipulation.
Stone Forest, China
Blade-like columns of limestone, many over 10 m tall, form a landscape that resembles a forest of stones. The region is a UNESCO World Heritage Site.
The stone forests formed some 270 million years ago in what was once a shallow sea. Sandstone and limestone accumulated in the basin, and was eventually pushed up into the air. The rocks were then shaped by wind and water to create these spectacular stone pillars.
Valley of the Moon, Argentina
Arid and rugged, this barren landscape looks like – you guessed it - the surface of the Moon. But it is actually a fossil graveyard.
The site contains undisturbed deposits from 250-200 million years ago. Fossils of some of the oldest dinosaurs, fish, amphibians, reptiles and over 100 species of plants have been found. There are also huge petrified tree trunks.
Wave Rock, Australia
This concave rock is 14 m high and 110 m long. It is part of the northern side of Hyden Rock, a giant granite outcrop over 2.7 billion years old, located in Hyden Wildlife Park in Western Australia.
The wave is believed to have formed by the action of running water on granite. The colourful streaks on its face are made of minerals left behind by rainwater run-off.
Chocolate Hills, the Philippines
There are about 1500 of these limestone mounds in Bohol province in the Philippines. They are normally covered by grass, but turn a deep-brown colour during the dry season.
In 1988, the Chocolate Hills were declared the Philippines' third National Geological Monument.
Giant's Causeway, Northern Ireland
These massive hexagonal black basalt columns rise like steps and interlock neatly. There are over 40,000.
They probably formed after volcanic activity 50-60 million years ago. The sizes of the columns were most likely determined by the speed at which the erupted lava cooled.
Bryce Canyon National Park, Utah
Located on the Colorado Plateau, the Bryce Canyon in southern Utah is a natural amphitheatre filled with spires and hoodoos. The Paiute Native Americans called it "red rocks standing like men in a bowl-shaped canyon".
The hoodoos were formed when water repeatedly froze and melted in the vertical cracks of sedimentary rocks. Some hoodoos are taller than a 10-storey building.
Vermillion Cliffs National Monument, Arizona
Popular among hikers, Vermillion Cliffs is a treasure trove of deep canyons and steep cliffs. It is also home to "The Wave" (pictured), which is made up of undulating sandstone.
The Monument is located on the Colorado Plateau, and gets its rich reddish hues from the sandstone that formed the landscape. The colours of the site change as the day progresses.
Cave of the Crystals, Mexico
This cave contains gigantic, sword-like gypsum crystals. It is 300m underground in the Naica Mine in the Mexican state of Chihuahua. It was discovered by two brothers drilling for lead and silver.
The enormous crystals are believed to have formed when gypsum-saturated groundwater flowed through the caves, and was heated and cooled by hot magma below. Some of the largest crystals may be over 500,000 years old.
San Andreas Fault, California
This is one giant fracture on the earth's crust, nearly 1,300 km long. The fault line began forming over 30 million years ago when two massive tectonic plates – the Pacific and North American – collided.
A major earthquake may well strike the San Andreas Fault in the coming decades.