Youtube conspirator MrMBB333 was combing through Google Earth when he spotted a strange bump in the seabed 90ft underwater, around a mile and a half from the coast of Long Beach in Los Angeles.
Sharing the discovery with his viewers, he points out what he believes to be the sunken city’s “perimeter wall”, as well as an entrance point for residents of the region.
He states how perimeter walls were a fairly common way of protecting cities in the past, including the Italian capital Rome in 275AD.
The “city” found on Google Earth is almost a mile long and half a mile wide.
Changing the satellite image’s filter, the theorist goes on to identify what he believes to be houses nestled within the walls of the city.
“You can tell it’s not something that’s just random – it was intelligently designed,” he said.
The bizarre video has gained more than 40,000 views since its upload earlier this week (November 26).
Some claim the strange marks on the seabed could be an underwater military base.
Sceptics have written-off the discovery as sand dredging to make concrete.
But most viewers are completely baffled as to how such a mystery could still exist in 2018.
One person wrote: “So we go to Mars to see what’s there, but have no idea whats one mile off our Californian coast?”
Another commented: “Divers, go and explore – it is answers we need, not speculation.”