What's the most popular air route in the world?

New York to LA? London to Paris? Beijing to Shanghai?

Chances are your first guess wasn't the domestic flight between Seoul and Jeju, the capital of Jejudo island in South Korea. Last year, almost 65,000 flights made the journey between the two cities. The next busiest air route, Tokyo to Sapporo, didn't even come close with just under eight million passengers.

Flights from Seoul to Jeju are so popular that you can board one every 15 minutes. There are around 250 flights that make the journey in either direction every day, according to Google.

Most of the tourism is domestic — Jeju is often touted as the "Hawaii of South Korea" — though it is not just Koreans that are lured by its beauty. In 2014, Jeju was behind the spike in Chinese tourists visiting the Republic of Korea, according to Chinese travel giant Ctrip. The Chinese are largely flocking to the island because of its visa-free entry requirements and abundance of casinos, which are banned in China.

The pictures below show why honeymooners and holidaymakers come in droves to bask in Jeju's natural beauty.