They let the mystery sink in.

A Michigan couple doing home renovations discovered a Prohibition-era, 20-foot-deep bootleggers’ tunnel beneath their home that was likely used for smuggling alcohol into the US.

Hayley Gilmartin and her husband, Trevor, who live on Lake Huron — a body of water separating the US from Canada — uncovered the eerie, water-filled room when removing an old, broken jacuzzi in the middle of their house.

The room is connected to the body of water by a six-foot pipe, Hayley recently told Newsweek.

Despite the “creepy” reveal, the two homeowners put on brave faces for what came next.

“We scuba-dived in the river and found the other end of it, which is a huge tunnel,” Gilmartin, 30, told Jam Press, noting that it is “impossible” to pump the water out because the room “is still getting water from Lake Huron and the rivers that it is connected to.”

The dark, concrete space is nearly empty, except for a support pole and wood-paneled wall that they believe connects to the tunnel system.

The couple, who bought the property in 2020, later learned several neighbors also have similar tunnels beneath their homes.

A near century ago, Lake Huron and the adjoining St. Clair River became critical waterways that boaters and crime syndicates used to bring in bootleg alcohol from north of the border.

The area was responsible for 75% of prohibition activity, according to experts.

Learning of their likely connection to gritty history, Gilmartin posted their sink-easy and scuba adventures to TikTok in clips that have racked up millions of views.

“I think anyone finding a manhole under their house in pitch darkness is going to find it spooky,” Hayley told Newsweek.

She added that removing a wooden wall in the water room may be their next project and promised more updates.

“We are going to keep exploring it, and if possible we will drain it and maybe create a game room or bowling alley lane down there,” Gilmartin told Newsweek.