Image by Strabag

Vancouver Broadway subway line - image by Acciona press release.

image: VINCI press release

Scheldt Tunnel imagination by Lantis.

Oosterweel link (Oosterweelverbinding) in Antwerp. By WCC.

Austria Semmering Basistunnel (base tunnel) - by Földhegy Wikimedia Commons

Underground City (Montreal Canada)  from Wikimedia Commons. I want to thank 'Laslovarga' for making this photograph available to public.

photo from Yangju city