[center]July 7th, 2020: A city has appeared overnight.

In the blink of an eye, towering buildings rose from beneath the waves. One moment, nothing; the next, that particular patch of international waters was home to a sprawling metropolis. Streets, perfectly maintained, are hemmed in on all sides by parks, apartments, shopping centers, with several suburban districts circling the urban areas. By all accounts, this new city--rapidly dubbed "Atlantis" by the immediate social media buzz--is a perfect account of a thriving economy.

Except Atlantis, for all its perfections, is completely deserted. Every satellite image taken has revealed empty streets and empty beds. Every radar scan has revealed nothing but open air and modernized buildings. Sonar has shown nothing below the city, either: the metropolis appears to float on a flat plate just below the surface.

After several months, Atlantis was eventually dubbed 'non-threatening' by the governments of the world. Despite the lack of reliable intelligence from the structure, there had been no attacks, no alien or foreign assaults. It was just...there. Sitting out in the middle of the Atlantic. Weather patterns seemed to steer clear of the city, with satellites noting the strange, and oftentimes magical ways the clouds bent around the city's perimeter. Expeditions were mounted, to see what mysteries the city held inside its shining glory. 

The real problem occurred only then: everyone who entered the city disappeared almost immediately. None have returned, including the Cessna 750 that decided to fly over the gleaming towers last month. Naturally, this has led to an explosive growth in Atlantean tourism. After the first few disappearances, most people have been smart enough--or cowardly enough--to avoid getting too close.

Most, but not all. For one reason or another, you find your way to the floating paradise, and to the mysteries within.[/center]

[hr]
An idea that cooked up in my head while I was procrastinating some other stuff today. Storyline is still flexible. No magical or scientific tropes have been ruled out as of yet

Time period: roughly modern-day. 
Rules: be cool or whatever, be willing to go with the flow, etc

I haven't done this in a while so I'm not sure if I'm forgetting anything, feel free to ask questions

[i]Previously named "Here Be Dragons", but was renamed for confusion.[/i]