Rochester MN: https://www.experiencerochestermn.com/planning-tools/getting...
Taipei Taiwan: https://pqvst.com/2023/05/28/taipei-underground/
New York NY near the World Trade Center: (can't find an up-to-date map or article)
Hong Kong near Central area: https://www.theguardian.com/artanddesign/architecture-design...
They are great as a way to avoid extreme weather on the surface (cold in Rochester's and New York's case, hot in Taipei's and Hong Kong's case) and car traffic.
Hong Kong takes things a step further in that it's actually hard to get around at ground level. Many streets don't have pedestrian crossings and there are barriers to prevent jaywalking. I'm not a fan honestly.