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This shot by Matthias Raabe shows the accelerator tunnel for Hera, the Hadron Electron Ring Accelerator, at Desy in Hamburg. The two-ring accelerator, which took six years to build before coming online in 1990, is the world's only electron-proton collider. The Hera tunnel runs for 6km at a depth of up to 25m.
Photo credit: Matthias Raabe/Desy