1. The "Door to Hell" gas fire in Turkmenistan ignited by scientists in 1971 has not stopped burning for 45 years.

2. 50,000 form "The Black Sun" in the UK before sundown in mid-winter.

3. The Enchanted River in Mindanao Philippines is so mysterious because no one knows where it comes from.

4. Tanzania's Lake Natron:

5. Tidal bores in the Amazon in Brazil and Severn in England.

6. Lenticular clouds are lens-shaped clouds that form in the troposphere.

7. Frost flowers or ice crystals are found on young sea ice and thin lake ice in cold and calm conditions.

8. The Richat Structure - known as the Eye of Africa, is a circular geological formation located in the middle of the Sahara Desert. No one knows how it came to be.

9. The Catatumbo Lightning happens 140-160 nights a year, with 10 hours per night, and 280 times an hour.

10. Underwater crop circles in Japan - created by male pufferfish when trying to woo a female.

11. The undulatus asperatus - a separate cloud classification.

12. The Flowering Desert in the Atacama Desert, Chile.

13. Circumhorizontal arcs happen when ice halo is formed by plate-shaped ice crystals in cirrus clouds.

14. Sailing stones - rocks move and inscribe long tracks along a smooth valley floor. No human or animal did this.

15. The Eternal Flames Falls in Chestnut Ridge Park, New York burns, without any gas. Scientists are unsure how it continues to burn.

16. Namibia's Fairy Circles. No one can explain them.

17. 40,000 interlocking basalt columns in Northern Ireland.

18. The Great Blue Hole off the coast of Belize is 1,000 feet across and 400 feet deep.

19. Spherical boulders in New Zealand.

20. 43 million land crabs migrate to lay their eggs in the ocean.