Just 20 years ago, there were only 3 tunnels in Korea longer than 3km. Since then, civil engineering tech has peaked, and long-ass tunnels are popping up everywhere. Right now, there are 13 tunnels over 5km! Let's look at the rankings for tunnels 5km and up. If the two directions have different lengths, I used the longer one.

13. Baehuryeong Tunnel 5,057m Opened in 2012. Connects Chuncheon and Yanggu on Route 46. It was the longest in Korea when it first opened. It's still the longest among non-motorway tunnels. Yanggu is such a rural part of Gangwon-do that the transport was dogshit; it used to take nearly 2 hours just to get to Chuncheon. The original road was submerged by the Soyang Dam and replaced with a super windy road. It finally got better in the 21st century.

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12. Yeongsan Tunnel 5,105m Opened in 2024. Crosses the border of Changnyeong and Miryang on the Hamyang-Ulsan Expressway. Named after Yeongsan-myeon. As I'll mention later, the Hamyang-Ulsan Expressway is an extreme 'bridge-and-tunnel' highway where tunnels make up over half the route. This is just the beginning.

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11. Incheon Bukhang Tunnel 5,420m Opened in 2017. Located on the Incheon-Gimpo section of the 2nd Ring Expressway. An undersea tunnel that goes straight under Incheon North Port from Jung-gu to Cheongna. Underground tunnels are still tunnels, so it's on the list. Use this to get from Songdo to Cheongna. Even though it's a highway, the limit is only 80km/h. Since it's undersea, the road gets wet often from condensation, which is a pain.

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10. Jinhae Tunnel 6,085m Opened in 2021. The longest tunnel on a regular road (not a highway). Couldn't find a good photo. It functions as a bypass for the entire Jinhae downtown area.

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9. Shinbulsan Tunnel 6,466m Opened in 2020. Located between Baenaegol IC and Seoulju JC on the Hamyang-Ulsan Expressway.

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8. Boryeong Undersea Tunnel 6,927m Opened in 2021. Connects Daecheon Beach and Wonsando. Designated as Route 77. Longest national road tunnel, longest free tunnel, and longest undersea tunnel. It made Boryeong and Taean much closer.

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7. Geumjeongsan Tunnel 7,190m Opened in 2017. If you take the Busan Outer Ring Expressway and cross the Nakdong River, you immediately hit this 7km tunnel through Geumjeongsan. Once it ends, you see the Nopo-dong bus terminal.

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6. Shinwol-Yeouido Underground Road 7,530m Opened in 2021. Still counts as a tunnel. It starts at the end of the Gyeongin Expressway (Shinwol IC) and goes 70m deep underground along Gukhoe-daero to Yeouido. That area was famous for insane traffic, so they dug deep to split the flow. It has a 3m height limit, but big trucks often miss the sign and block the entrance. FYI, they're doing a separate project to turn Gukhoe-daero itself into an underground park, so it's still a construction zone.

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5. Munmu the Great 1 Tunnel 7,543m Opened in 2016. Located between South Gyeongju IC and East Gyeongju IC on the Donghae Expressway. Lots of mountains on the way to the East Coast from Gyeongju, so it's pretty long. Originally called Yangbuk 1 Tunnel, but the town changed its name to Munmu the Great-myeon in 2021, so the tunnel got a name change too.

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4. Jaeyaksan Tunnel 7,982m Opened in 2020. Yet another Hamyang-Ulsan Expressway tunnel. It connects right after the Shinbulsan Tunnel mentioned above. There's another 5km+ tunnel in the Hamyang-Changnyeong section that isn't open yet. Once the whole thing opens later this year, there will be four 5km+ tunnels in a 120km stretch.

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3. Namhansanseong Tunnel 8,345m Opened in 2025. Part of the Sejong-Pocheon Expressway. Longest among 3-lane tunnels. It literally goes straight under Namhansanseong, which caused some environmental drama.

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2. Seobu Ganseon Underground Road 9,363m Opened in 2021. Opened the same year as the Shinwol-Yeouido one. It's part of the U-SMARTWAY project Mayor Oh Se-hoon planned during his first term. They're planning to underground the Dongbu Ganseon and the Naebu Sunhwan roads too. It was built to fix the 'Seobu Ganseon Hell' traffic, but honestly, it's still hell. Plus, there are no exits in the middle, so if it gets jammed, you're stuck until the end. Meanwhile, they tried to cover up the original Seobu Ganseon road since it's no longer a motorway, but luckily that failed.

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Extra: Not open yet, but coming soon so I'm including it.

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Mandeok-Centum Underground Road 9,620m Busan's version of the deep underground roads in Seoul. It connects from the end of the Namhae Expressway in Mandeok-dong, goes under Oncheoncheon all the way to Centum City, and eventually links to the Gwangan Bridge. Expected opening: February 2026. And finally, the #1 spot!

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1. Inje-Yangyang Tunnel 10,965m Opened in 2017. Located on the Inje-Yangyang border of the Seoul-Yangyang Expressway. Has held the title of Korea's longest tunnel for 8 years. How can a tunnel be 11km long?! It's on another level. I've never been, but at 100km/h, it must take 10 minutes just to get through. However, this record will be broken eventually. The Jecheon-Samcheok Expressway just passed its feasibility study. It goes through the rough Jecheon-Yeongwol-Taebaek-Samcheok area (Route 38), and a 12km tunnel is planned. It just passed the study, so construction is far off; we'll probably have to wait 10 years. Out of 13 tunnels: 4 in Seoul Metro, 2 in Gangwon, 1 in Chungcheong, 6 in Gyeongsang. One highway even has three of them. Jeolla-do doesn't even have a 4km tunnel, let alone 5km. It's mostly plains, so there are no mountains big enough to need massive tunnels. For example, on the Honam Expressway, once you pass the Honam Tunnel into Jeonbuk, there are zero tunnels until the end. When I was a kid, the 4.6km Jungnyeong Tunnel was the longest, but now it's not even in the top 15. It'll keep dropping. Still, holding the record for 11 years was impressive. I also looked into railway tunnels. Railway tunnels are in a different league. There are 10 over 10km. I'll just list the top 5 to keep it short. (Subways don't count here).

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5. Baekun Tunnel 14,239m Opened in 2021. On the Jungang Line between Wonju and Jecheon. The Jungang Line was completely overhauled for double-tracking. There are three tunnels over 10km. In railways, the Jungnyeong Tunnel was the longest for 30 years, but even the new 11km Jungnyeong Tunnel is just fodder now.

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4. Solan Tunnel 16,240m Opened in 2012. On the Yeongdong Line between Dongbaeksan and Dogye. Longest tunnel that isn't for high-speed rail. Famous among train nerds because there used to be a switchback here. The elevation drop was too steep (800m to 50m) for a straight line, so trains had to zig-zag. They fixed that by building this spiral tunnel.

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3. Geumjeong Tunnel 20,323m Opened in 2010. A whopping 20km! Longest railway tunnel when it opened. To get the KTX through Busan city for the second phase of the Gyeongbu High-Speed Line, they just made the whole thing one big underground tunnel. Trains leaving Busan Station spend the first 10 minutes in total darkness.

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2. Daegwallyeong Tunnel 21,755m Opened in 2017. For the Gangneung KTX during the Pyeongchang Olympics. Daegwallyeong is so rugged that the highway has to loop around, but the railway just pierces straight through. To do that, it skips Daegwallyeong-myeon and starts right after Jinbu Station. So to get to the Olympic ceremony, you had to take a shuttle from Jinbu. Fun times.