On a dark winter’s night decades ago, a group of 50 men gathered for a lecture inside a stately old St. Paul mansion.

The speech, which was about recovery from addiction, took an unexpected turn when there was a noise from beneath the dining room, followed by puffs of black smoke.

Suddenly, a floor tile burst open like a trap door, and a man with a soot-stained face popped out.

The man — who seemed as shocked and confused as those attending the lecture — looked around for a moment before disappearing into the caverns below. He was never seen again.

“We usually said: ‘Myth or not myth?’ ” said Terri Hayden, executive director of Hazelden St. Paul, about the tale.

Turns out that it’s true.

It’s just one example of how caves beneath the old William Banholzer House — a structure that Hazelden has used since the 1950s — have affected life on the surface for decades.

This year, Hazelden completed a $26 million expansion in St. Paul that included $1 million for restoration of the landmark structure in the city’s West 7th neighborhood. Before the work could begin, Hazelden had to map the network of caves and tunnels beneath the property and, ultimately, change the shape and location of the new structure.

“There were lots of things that were pushing and pulling on the form of the building as you see it now,” said Donovan Nelson, the project designer from Minneapolis-based HGA Architects and Engineers. “The caves were no small part of that.”

Hazelden Foundation was created in 1949 in Center City, Minn., as a source of addiction treatment for alcoholics. During the early 1950s, it opened a halfway house for men in St. Paul called the Fellowship Club. By the decade’s end, that halfway house was relocated to a mansion originally built by a beer maker.

William Banholzer’s brewery churned out roughly 12,000 barrels per year at its peak. Called North Mississippi Beer, it was a popular brew in the 1880s, produced in one of many brewhouses that lined the Mississippi River in St. Paul, where sandstone caves were perfect for cooling kegs.

In 1958, Hazelden acquired the mansion, which Twin Cities architecture critic Larry Millett described as “a late, abstracted version of the French Second Empire style, with a high-hatted tower that presides over the neighborhood.”

Over the years, Hazelden built additions off the back of the mansion to increase its capacity for residential and outpatient services. The recently completed expansion included demolition of the previous 12,500-square-foot residential building, and replaced it with a 55,000-square-foot structure with 55 residential beds plus space for meeting rooms, offices and outpatient services.

While very contemporary, the new building incorporated architectural elements that invoke the old mansion — from its mansard roof and central turret to bricks and decorative wood panels. But it’s far from a carbon copy.

“We didn’t want to bring something that was overly historic into the new building,” said Nelson, the project designer. “Once you start to copy the old, you’re doing a disservice.”

While it had long been known that there were tunnels under the mansion, exactly how many and where they were had to be determined before construction could start.

In April 2014, an engineering firm located four large tunnels, five small tunnels and several intersecting passages.

Hazelden sealed them off so people couldn’t sneak in and get hurt during construction of the new building.

As initially conceived, the structure would have had more of an L-shaped configuration, and would have been situated on the lot closer to the river. The shape and location were changed to eliminate overlap with the caves, resulting in a larger backyard. It includes a labyrinth and a walking path that highlights each of the 12 steps toward addiction recovery, which are central to Hazelden’s method.

The 12-step method, as it turns out, was the lecture topic when the man popped out of the dining room floor. Former Hazelden employee Dave Kelly was giving that talk in the late 1980s. The man’s appearance was short — just long enough for everyone in the room to gasp.

Then, he quickly replaced the tile and returned to the network of caves, said Kelly.

How do you transition back into a lecture after a guy pops out of the floor?

The soot suggested the man had been making fires in the caves to stay warm, Kelly said.

“So, I said: ‘Let’s remember him in spirit, because he’s obviously struggling.’ 

“It just raised everybody’s awareness that … here’s a poor man living in the cave,” Kelly said.

 

Star Tribune researcher John Wareham contributed to this report.