The Pentagon’s research arm turned Twitter into a Craigslist post on Wednesday, soliciting the country for lightly used urban tunnels and underground facilities “able to host research & experimentation.”

There was a deadline: Friday at 5 p.m. Eastern time.

But to do what exactly?

In its tweet, the Defense Advanced Research Projects Agency, better known as DARPA, didn’t exactly spell out why it needed vast networks of “university-owned or commercially managed” space to turn into temporary development lairs.

Perhaps most famously, DARPA’s research led to what we know as the Internet — which means the agency developed technology in the 1960s that it used to bewilder large swaths of the public in 2019.

So what do they want?

First, there was confusion as to why the agency needed such facilities in a short amount of time, deepening the mystery of the request.

The agency posted photos of descending escalators and dank subterranean hallways dotted with trash and hanging wires as if they were rejected set locations from “Us,” the Jordan Peele film where twisted doppelgängers underground hatch plans to take over the above-world.

A quick Google reverse image search reveals a photo that has circulated as a free use photo for years (helpful search clues: “gloomy,” “a mess”).

“The ideal space would be a human-made underground environment spanning several city blocks w/ complex layout & multiple stories, including atriums, tunnels & stairwells,” DARPA said in a second tweet. “Spaces that are currently closed off from pedestrians or can be temporarily used for testing are of interest.”

Almost instantly, fans of the sci-fi show “Stranger Things” made reference to the monster from another dimension that tunnels underneath the fictional town of Hawkins, Ind. “Please,” DARPA rebuffed one fan. “Demogorgons are such a Department of Energy thing.”

Then, later, came the speculation. DARPA has long been interested in ways military and first responders are able to maneuver inside tunnels, caves and underground facilities.

The stakes and mind-boggling complexities for rescuers was made clear last year in Thailand, when 12 children and their soccer coach were trapped in a cave, prompting an enormous and successful rescue.

Meanwhile, the U.S. military has bet that future conflict will unfold in megacities and their seemingly endless and claustrophobic knot of tunnels, sewers, subway lines and facilities where enemy troops can move and attack without fearing airstrikes or artillery.

The Army has poured half a billion dollars to overhaul how infantry can move where the enemy expects them to move, communicate in an environment where radio transmissions may prove futile, and orient themselves in a place where a GPS — another DARPA project — would be useless. In that environment, night vision goggles that rely on ambient light may be useless, air can be toxic and enemy traps could lurk anywhere.

It’s not a new concept. Viet Cong-dug tunnels helped militants vanish and outflank U.S. troops, Navy SEALs flushed out militants in Afghanistan caves early in that war, and the Islamic State has burrowed into safety.

But now, China, Russia and North Korea could use a similar network to house command and control, mobilize troops and even launch planes from underground runways, Military Times reported.

Enter DARPA’s Subterranean Challenge, dubbed “SubT Challenge.”

DARPA finally revealed in a tweet a day later as the source behind its request: a competition that will help them develop “novel approaches to rapidly map, navigate, and search underground environments during time-sensitive combat operations or disaster response scenarios.”

The competition will hand out about $5 million in prize money to teams competing in various circuits and recently, eleven teams from eight countries completed a circuit in a Pittsburgh mine.

“With them, they brought 20 unmanned aerial vehicles, 64 ground robots and one autonomous blimp robot named Duckiefloat,” DARPA said.

The agency had already posted the request on its website on Aug. 20 in search of an environment suitable for the next challenge in February, Jared Adams, a DARPA spokesman, said in a statement Thursday.

The tweets “were a reminder of the upcoming deadline to respond,” Adams said, referring to posting on a clunky government website that few outside Washington have likely heard of before.

Adams told BuzzFeed News in a statement that it received few responses and turned to social media for help, creating the temporary freakout.

Who can blame the inventors of the Internet for that?

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