At 110 km in length (68.3 miles), Stockholm's tunnel rail system is said to be the world's longest art gallery. Over 150 artists have tried their hands decorating these. From paintings and mosaics to engravings and sculptures, the beautiful underground artwork done at these metro stations makes them the coolest metro stations in the world.

Amaze yourselves with these stunning photos:

1. The cave-like Solna Centrum subway station

Source: Bored Panda

Source: Bored Panda

2. And this is the wonderful Duvbo subway station

Source: Bored Panda

Source: Bored Panda

3. The amazing mural paintings at the T-Centralen

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4. Here is the stunning Solna Strand

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5. And the breathtakingly colourful Kungsträdgården

Source: The Guardian

Source: Bored Panda

6. The amazing Skarpnäck subway station

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7. And the beautiful Huvudsta subway station

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8. This is Stadion, the rainbow-inspired subway station

Source: DailyMail

Source: DailyMail

9. And here we have the surprisingly beautiful Akalla subway station

Source: Bored Panda

Source: Bored Panda

10. This is the stunning Universitetet

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11. This fiery pit is called the Rådhuset

Source: Bored Panda

12. Here's the futuristic Tekniska Högskolan

Source: Bored Panda

Source: The Guardian

Source: The Guardian

13. The sailing boat at the Fridhemsplan

Source: The Guardian

14. The oh-so-spectacular Östermalmstorg

Source: The Local

15. And here at the Högdalen, you can find tulips waiting for you.

Source: The Guardian

Unbelievable, aren't they?