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This famous alleyway in the Susukino entertainment district is crammed with ramen shops, including branches of several venerable Hokkaidō shops. It's been around since 1952, and is keen to distinguish itself from all the 'imposter' ramen alleys.
It can be a little tricky to find (old as it is, it doesn't glow as bright as everything else in Susukino), but all locals know where it is. Look for 'Ganso' as there are other ramen alleys nearby. Hours for individual shops vary.