Commuters passed above it for decades without knowing what lay beneath. Now, a 335-meter underground passage in the heart of Seoul has taken on a new identity. Closed to the public for more than four decades, the tunnel connecting Euljiro 1-ga and City Hall stations on Seoul Metro Line 2 officially reopened Monday as K-Culture Station, launching with “COSMOS,” an immersive exhibition marking the 20th anniversary of K-pop group BIGBANG. Inside the darkened space, large digital screens display colorful digital portraits of the members, while bright yellow crowns — a symbol long associated with BIGBANG — glow across the black floor. The exhibition reimagines the group's two-decade history through light, video and sound across 11 experience zones featuring media art, projection mapping, holograms and interactive displays. “For more than 40 years, a 335-meter underground space lay closed beneath City Hall Station, one of the city’s busiest transit hubs,” Seoul Mayor Oh Se-hoon said, after passing through digital screens, music and mirrored installations at the K-Culture Station