Gary Holmes has had a 20-year love affair with the old Milwaukee Road Depot.

Holmes’ development company, CSM Corp., has poured a little more than $100 million into the purchase and renovations of the complex over the last two decades. The former train hub in Minneapolis’ Mill District is now is in the middle of a long-awaited final phase of its transformation as a hospitality and event center, scheduled to be finished by early next year.

“I had a fascination with old buildings and loved old buildings,” said Holmes, president and chief executive of CSM. “[At times] we had so many different people working [on the Depot], there was no way to know what the costs even were, but we just kept going. Every time we did something, we found a way to make it more splendid.”

New renderings revealed this week show plans for the event space in the former train shed, expanded 24,000 square feet with boardrooms, a large glass-encased ballroom and an outdoor eating space complete with colored tile that echoes the depot’s original train rails.

As of this week, the foundation system has been constructed and workers have started masonry and window-frame installation. Bookings are already underway for the complex, though it isn’t scheduled to be complete until January.

The Milwaukee Road Depot was constructed in 1899 and designed by Charles Frost, who was the architect behind several other train terminals across the country including the Union Depot in St. Paul. The Depot served as the end of the line for the Chicago, Milwaukee, St. Paul and Pacific Railroad Co. At its peak in the 1920s, the Depot had 29 trains departing daily.

In 1971, the last train left the Depot, and some of the building was converted into office space. Years later, the Depot and the nearby freight house were placed on the National Register of Historic Places.

Several developers had shown interest in possibly converting the Depot to other uses, including Holmes. However, the Resolution Trust Corp. — the government agency formed in the 1980s to liquidate assets of failed financial institutions — eventually sold the Depot and the seven blocks around it to the city of Minneapolis for $2 million.

The complex decayed for years, with much of the surrounding area serving as surface parking lots. Holmes was then approached by Mayor Sharon Sayles Belton about redeveloping the Depot. At first, he was not interested.

But Holmes eventually agreed. CSM bought the building and land in 1999 and began a massive renovation that would take until 2001 and result in the creation of the Renaissance Minneapolis Hotel, the Depot event space, the Residence Inn, parking ramp and nearby office center, where CSM would move its offices.

To say the Depot was a mess when CSM took hold of it was to put it mildly, Holmes said.

The city had done some environmental remediation work to help clean up the oil and grease from the trains, but the land was still polluted.

Workers went through the building with flashlights and found communities of homeless people and pigeons living in the upper floors and underground caverns.

“All of this area was risky and was very challenging,” he said. “There was a lot of crime.”

No expense was spared for the renovations. Workers had to lie on their backs on top of scaffolding to repair the ceiling of the complex’s Great Hall, which served as the former lobby of the original train depot. A local father-and-son duo honed the marble floors in the Great Hall more than a dozen times to get the surface as smooth as possible, though there are still worn areas where travelers once waited in line for train tickets.

During the Depot’s original restoration, Holmes commissioned a painting by New York artists of a train going over the Stone Arch Bridge. Spanning more than 20 feet, the art piece had been applied directly to a wall slated for demolition in the latest round of renovations, but instead Holmes ordered the wall to be moved to another portion of the complex.

“Obviously that wasn’t called for — nor was it to spend all of the money that we did to restore the ceiling — but if you are going to go for it, you are going to go all the way,” Holmes said.

The Depot helped pave the way for future development along Washington Avenue S., which has seen a surge of new construction proposals for the corridor’s last remaining surface lots in recent months.

“Nobody would even consider doing anything down here,” he said. “Everybody said we changed all of that, and we did. We really did. It wasn’t without challenges, but we did.”

In the truss-roofed train shed, CSM installed an ice rink, which was covered for special events. On some nights, Holmes would bring friends to skate in the dark with just the city lights for illumination.

“It was just magical,” he said.

While Holmes liked having the ice rink, it was costly, and the company lost about $400,000 a year to keep it open and maintained.

Like many ice-rink operators who have had to assess how to retrofit their cooling systems due to the phaseout of the commonly used refrigerant Freon, Holmes decided to close the rink last year instead of renovating it. With the rink closed, it opened up possibilities to do other things with the space.

In the current $9 million renovation, which follows improvements made in 2016 when 110 hotel rooms were added to the complex and a water park removed, the hotel will incorporate artifacts from the Milwaukee Road Depot along with bronze life-size statues of rail workers.

Asked if all the money and time was worth it, Holmes laughed and said to ask him in three years.

“It’s something more to give back to the city,” he said.