Solving riddles of Gyeongui tunnel beneath Hongdae area
The area around Hongik University in western Seoul, commonly called Hongdae, has seen major changes over the decades. But rather than originating from the arts university sitting on a mountainside overlooking the neighborhood, most changes here have been driven by infrastructure development.
This became apparent to me after roaming through tunnels being dug for subway infrastructure around Hongdae, while a thin metal deck high above my head thundered with the passing of every vehicle on the road surface above.
The neighborhood saw its most recent transformation with the arrival of the Airport Express (AREX) line in December 2010 and the Gyeongui (now Gyeongui-Jungang) Line in December 2012. Much of the area was overrun with construction until relatively recently, with the opening of Gyeongui Line Book Street in late 2016 and AK Plaza in August 2018. Before then, Hongdae’s development was corralled on one side by construction.
Trains have been passing through this area since 1905 with the opening of the Gyeongui Line connecting Seoul with northern Korea. Back when I was new in Korea in the early 2000s, train tracks still ran through the area revealing the Gyeongui Line’s former course. But a new plan was to breathe new life into this historic train line by relocating it underground.
By 2008, construction fences were in place to hide the tracks, while a deep trench was excavated for the new tunnels.
Wandering into a construction site one day around 2010, I discovered a pit leading underground, outfitted with metal stairs and lights conveniently left on. Gradually I found that nobody was down there at night to stop people like me, so over repeated forays I went deeper and deeper. The ground at the bottom was mostly dirt, and I found the entrance to a large cylindrical concrete tunnel. Following down that, I reached a massive machine filling the circumference of the tunnel, being used either to form the concrete interior surface of the tunnel or polish it.
I found other entrances along the length of the Gyeongui tunnel excavation, allowing entry and escape in multiple locations, either through subway vents or stations such as Hongik and Sogang. Over the course of various visits, my shoes touched every section of the tunnel from where it goes underground around Gajwa Station in the northwest to somewhere beyond Gongdeok Station in the southeast.
I got to see the construction progress through multiple visits. I saw how they shaped it, added rebar, poured concrete, put tracks in and added other infrastructure. Much of the tunnel construction consisted of digging a long trench and then covering it up again, a simple but disruptive process that nonetheless got the job done.
After train services began in late 2012, I discovered some of my secret entrances still open. It was possible to go down to a vent room beside the tracks and watch the trains speed by. Trains were infrequent before the Gyeongui and Jungang lines were merged, and I used to have a rule: stay for two trains and then leave.
In March 2013, I was bored one weekday night so I visited alone. I took a wrong turn and entered a ventilation room. The floor was covered in grills overlooking the train tunnel below, and the walls were occupied with massive vents allowing air to rush through, reducing wind resistance for incoming trains. When I went to leave, I found the door had locked behind me. I was trapped.
Fortunately I had some cell reception, and was able to text an SOS to a friend living nearby who shared my interest in hidden places. He arrived to release me within 20 minutes. If it weren’t for that phone signal, I might still be down there now, six years later.
There are various hidden dangers inside subway tunnels, which is why I never publicly share current information. One wrong move can be lethal. This is not a leisure activity, unless safety preparation is your idea of fun.
An urban explorer waves a flag inside a tunnel beneath the Hongik University area in 2013.