Jamsu, the Han River deck built to go underwater, where music videos keep returning

You have seen this bridge without knowing its name. Two people walk a flat grey deck that sits almost level with the river, the water sliding past close enough to touch, the far bank stacked with apartment lights that smear when the camera moves. There is no traffic in the frame and nothing tall to fall from. In a city full of high things to shoot down from, the music videos keep coming back down here, to the one bridge in Seoul built low enough to go under.

The bridge built to disappear

The structure has two names because it has two decks. The upper level, well above the water, is Banpo Bridge (반포대교, Banpo-daegyo), an ordinary river crossing full of taxis. The lower level, riding just above the surface, is Jamsu Bridge (잠수교, Jamsugyo) — jamsu means to submerge or to dive, and the name is not decorative. When the Han (한강, Hangang) swells after the summer rains, the deck goes under, and the city lets it.

That was the design. Finished in 1976, years before the upper deck was set on top of it, the low bridge was built flat and cheap on purpose, a crossing meant to flood rather than fight the water. On dry days the lower deck still carries cars, but on warm-season Sundays the city closes parts of it to traffic and hands the surface to walkers and cyclists, and the vehicles vanish from the shot. The height that makes it useless in a storm is exactly what drops a camera to eye level with the river.

The fountain the camera cannot resist

Along both flanks of the upper deck runs the Moonlight Rainbow Fountain (달빛무지개분수, Dalbit Mujigae Bunsu), which Guinness once recorded as the longest bridge fountain in the world at roughly 1,140 meters. Close to two hundred tons of water a minute are pulled straight from the Han, pushed out through nozzles the length of the span, and dropped in lit arcs some twenty meters down toward the low deck. From Jamsu you stand beneath the falling edge of it.

It runs from around April to October and shuts off for the cold months, so for half the year the shot simply is not available. In season there is usually a midday show and a run of evening ones — roughly 7:30, 8:00, 8:30 and 9:00 — each about twenty minutes, the colours cycling to recorded music. It costs nothing to watch. The water carries a faint smell of the river, which no video will tell you.

Standing where the camera stands

The frame you remember is shot at dusk, in the twenty minutes when the sky still holds blue and the towers begin switching on. Come at least half an hour before sunset and walk out onto the low deck from the Banpo (반포) side; the composition everyone uses is the flat line of the deck running toward the fountain, water on both sides, the south bank glowing behind. From the deck the arcs fall toward you. From the grass of the south bank you get the whole curtain at once.

Renting one of the city's pale-green Ttareungi (따릉이) public bikes makes the distances reasonable — about 1,000 won for an hour, unlocked by app — because the riverside paths run long and the bridge is only one stop on them. Cross to the north bank and back and you have ridden through two districts. Keep to the marked bike lane on the deck; on car-free Sundays it fills fast, and the joggers do not always look.

The camera keeps the bridge and throws the crowd away. Stand on it at dusk and you get both.

The park behind the shot

What the videos crop out is the picnic. Banpo Hangang Park (반포한강공원, Banpo Hangang Gongwon) spreads along the south bank, and on any warm night it is a field of mats, low tents and delivered fried chicken. The convenience stores here keep the ritual Seoul is quietly known for: buy a packet of ramyeon (라면), pay the machine, and cook it yourself in a coin-operated boiler for a couple of thousand won, then eat it cross-legged with the fountain going off behind you.

You can rent a mat and a small shade tent from stalls near the water for a few thousand won, and the phone numbers taped along the railings will bring chicken and beer to a spot you describe by landmark. None of this is romantic in the way the footage is. It is better, because it is the version with other people in it.

비가 많이 온 다음 날, 잠수교는 정말로 물에 잠긴다.

Getting there, and the night it isn't there

The nearest gate is Express Bus Terminal station (고속터미널, Lines 3, 7 and 9); leave by exit 8-1 and follow the underpass signs for Banpo Hangang Park, about ten minutes on foot. Sinbanpo (신반포) on Line 9 lands you closer to the water if the bridge is all you came for. Walking the deck and watching the fountain cost nothing; a bike runs about 1,000 won an hour and a cooked ramyeon around 1,500.

Go on a dry evening between May and September, arriving before sunset for the light and staying for the first evening fountain. The mistake to avoid is the obvious one people still make: after heavy rain the Han rises and the low deck genuinely goes under — closed, gone — and through winter the fountain is switched off entirely. Check the month before you build a night around it.