The Secret Ancient Tunnels of the Americas, etc.

 https://inexplicata.blogspot.com/search?q=The+Tunnels+of+the+Americas 

https://www.imdb.com/title/tt0060036/mediaviewer/rm3013509121

https://unchartedruins.blogspot.com/2018/07/the-secret-tunnels-of-ancient-mexico.html  

"During the California heat wave of 1906, Baldassare Forestiere dug a home underground with just a pickax and shovel. He spent 40 years excavating 10 acres of rooms..." https://www.youtube.com/watch?v=mUKRPoQKynk Quite a nice, do it yourself underground complex.

Coober_Pedy, Australia https://www.youtube.com/watch?v=MCXnKgSr1N0 , https://en.wikipedia.org/wiki/Coober_Pedy#Tourism , https://www.youtube.com/watch?v=ihn-jWnOWwI

"The Krell machines in Forbidden Planet are a vast underground computer complex built by the advanced but long-vanished Krell civilization." https://www.facebook.com/groups/forbiddenplanetmovie/posts/10163715398958777/ 

https://themoviejunkie.medium.com/the-forbidden-planet-retro-futurism-at-its-best-d58cb42e76fb

https://nzpetesmatteshot.blogspot.com/2011/03/forbidden-planet-shakespeare-in-space.html

And more not so ancient stuff. 

https://www.reddit.com/r/RetroFuturism/comments/115igaw/the_time_tunnel_1960s_tv_show_time_machine , https://www.imdb.com/title/tt0060036/mediaviewer/rm413040641 

A documentary about the classic 60's Sci-Fi series 'The Time Tunnel'. https://www.youtube.com/watch?v=3MByhY6aSUo 

https://scifi.stackexchange.com/questions/196445/what-was-the-length-of-the-time-tunnel-in-irwin-allens-60s-sci-fi-tv-series

 It all started deep, down in the desert...  

https://www.facebook.com/groups/classic.television.shows.group/posts/1436470110334314/

https://en.wikipedia.org/wiki/Underground_city

Underground Tunnels and Cities https://www.youtube.com/watch?v=g8V2u7YT02w  

https://en.wikipedia.org/wiki/Path_(Toronto)#Early_pedestrian_tunnels

https://www.reddit.com/r/todayilearned/comments/xpg1io/til_according_to_guinness_world_records_path_a/

https://www.reddit.com/r/askTO/comments/1rq9xnu/how_does_the_r%C3%A9so_in_montreal_compare_to_the_path/ 

https://en.wikipedia.org/wiki/Subterranean_New_York_City

https://en.wikipedia.org/wiki/Chicago_Pedway#History

https://en.wikipedia.org/wiki/Underground_City,_Montreal