Answer: Montauk

Stranger Things focuses on, well, strange things happening in the small town of Hawkins, Indiana and the events that surround the local government-run Hawkins National Laboratory. With an aim at divulging as little spoiler material as possible, a key component of the show is secretive government experiments conducted on citizens with some very peculiar sci-fi results.

With that in mind, it should come as no surprise to anyone that writers for the show drew on conspiracy theories surrounding actual government experiments and facilities. One particular source of such information apparently had quite an influence on the writers: the alleged experiments, dubbed The Montauk Project (a supposed extension of the conspiracy theory based Philadelphia Experiment), carried out at Montauk Air Force Station at Montauk Point, Long Island.

As the theory goes at least, the experiments were carried out for the purpose of developing psychological warfare tools and even included fringe research into time travel, teleportation, mind control, and more. The conspiracy theory and allegations surrounding it are, naturally, unsubstantiated in terms of actual evidence or official statements on the matter. The photo shown here is of the abandoned radar installation and some of the outer buildings at the facility on Long Island.

In light of that, the writers of Stranger Things gave the TV show a working title of Montauk in allusion to the alleged experiments and the way such government experiments played a role in shaping the events in Stranger Things.