Coober Pedy, South Australia (??????????)  [source:Huanqiu]

Wieliczka salt mine, Krakow, Poland (?????????????) [Source:Huanqiu]

The Paris Catacombs, France (?????????) [Source:Huanqiu]

Cappadocia, Turkey (?????????) [Source:Huanqiu]

Mary King's Close, Edinburgh, Scotland (????????????) [Source:Huanqiu]

Seattle Underground, Washington, United States (????????????) [Source:Huanqiu]

G-Can flood surge tunnels, Tokyo, Japan (?????????) [Source:Huanqiu]

Shanghai Tunnels, Portland, Oregon, United States (??????????????) [Source:Huanqiu]

Greenbrier Bunker, West Virginia, United States (??????????????????) [Source:Huanqiu]

Cu Chi tunnels, Vietnam (???????) [Source:Huanqiu]

Moose Jaw, Saskatchewan, Canada (?????????????) [Source:Huanqiu]

City of Caves, Nottingham, UK  (??????????) [Source:Huanqiu]