For most of the 20th century, grand old houses in St. Paul’s historic Ramsey Hill district often were divided into apartments or put to other uses. Realtor Sarah Kinney says a countertrend gathering steam since the 1990s has been their conversion back into single-family homes.

There is no more spectacular example than the Louis Hill house, next door to the landmark James J. Hill house on Summit Avenue. Designed in 1901 by architect Clarence Johnston for Louis, a son of railroad tycoon James J., then doubled in size by a 1912 renovation, the 25,000-square-foot mansion remained in the Hill family until 1954. From 1961 to 1997, it was a retreat for Catholic nuns. In the late ‘90s, an organization called the Deva Foundation began to remodel it as a children’s hospice, but gave up in the face of mounting costs.

In 2001, with Kinney as their real estate agent, Richard and Nancy Nicholson of St. Paul bought the Louis Hill house for $1.7 million. Though the nuns were excellent caretakers, Richard Nicholson says, the couple spent “a lot more than that” renovating the place. Among other things, it needed a new roof, and “all 104 storm windows had to be replaced.”

The Nicholsons emerged with what is now a private residence of jaw-dropping grandeur. The second-floor ballroom can seat 200 for dinner and houses a full-scale working pipe organ as well as a pair of grand pianos. Even the basement swimming pool and changing rooms have been restored to their 1912 elegance.

The house’s history has special resonance for the Nicholsons. Richard’s great-grandfather, early 3M investor and president Lucius Ordway, was a friend and associate of the Hills. Ordway went to parties in the same ballroom the Nicholsons now use to host civic groups. (Noted benefactors, they are the reason the restored main reading room of the St. Paul Central Library is called the Nicholson Information Commons.)

Caught up in restoration fever, the couple then bought and renovated another Summit Avenue mansion. The Lightner house, designed by Cass Gilbert in 1893, had been divided into apartments for decades. The Nicholsons used top local designers to turn it back into a single-family home. Last fall, via Kinney, they sold the Lightner house to John Fallin, president of Feed Products North, Inc., of Maplewood, for $2.1 million.

“I spent more than double that [to buy and renovate it], so I had a nice loss,” Richard Nicholson says ruefully.

Despite fairly compelling evidence that for him, historic real estate might not be a money-making proposition, Nicholson got a realtor’s license and now works part time as a colleague of Kinney’s at Coldwell Banker Burnet. “I became a realtor vowing that I’m done doing this with my heart, and from now on I’ll do it with my head,” he says. “We’ll see.”