A bizarre overnight incident in Brooklyn has prompted an investigation after more than a dozen people were spotted climbing into and out of New York City ’s sewer system.

According to the New York Police Department , the first incident unfolded in the neighborhood of Gravesend on Thursday (May 28). Authorities say several individuals were seen entering a manhole around 11 p.m. before resurfacing roughly three hours later.

Hours later, police received reports of a second group using another manhole approximately eight miles away. Investigators say the group descended underground shortly after 1 a.m.…