The dilapidated Clemens Mansion just north of downtown looks like a horror movie set…. Nightmare on Cass Street. With its faded antebellum columns, collapsing porches and lean-to construction, it seems likely to fall over (or fall in) at any minute.

It’s hard to believe that this decrepit old house is set to become a centerpiece — a “legacy” property — of the $8.1 billion north side redevelopment plan proposed by developer Paul McKee.

Central West End developer and rehabber Bob Wood is partnering with McKee on the project, which will turn the 150-year-old mansion and adjoining chapel into senior apartments and community center.

“We’re talking to the Missouri History Museum housing a museum honoring the heritage of the surrounding neighborhood,” said Dan Holak, who is heading up the project for Wood. “They would occupy part of the chapel building and we’re also talking to the Missouri Botanical Garden about doing some landscaping and putting in an urban garden.”

For years, McKee secretly bought more than 850 properties on the city’s near north side in a two-square-mile area. He announced last year the redevelopment plan and is negotiating nearly $400 million in tax increment financing with the city of St. Louis. He said he plans to turn the mostly vacant properties into 10,000 new homes and millions of square feet of office, warehouse and retail space to the area over 15 years. At the end of last year, the Missouri Department of Economic Development awarded McKee $20 million in tax credits for the project. McKee bought the Clemens mansion in 2005.

Wood is also hoping to finance the $13 million Clemens project through historic and low income tax credits. A model for the development is Wood’s work on the Franklin School at 814 N. 19th Street. A former St. Louis public school, designed by famed school architect William Ittner and opened in 1911, Franklin was closed in 1995. Wood renovated it into 75 senior apartments and reopened it in the growing neighborhood now known as Downtown West in 2007.

“The condition of Franklin School when we started there was pretty nasty,” Holak said. “With funding, we’re confident we can make the Clemens mansion work.”

I met with Holak and architect David Lorentz at the Clemens mansion on a cold December afternoon.

At first, I was content to just walk around the outside of the property, which includes the 55,000-square-foot mansion, an addition on the back of the house, and an adjoining 3,000 square foot chapel building. Wood’s plan, Lorentz said, is to convert the main house into 49 senior apartments. The first floor of the chapel would be residential, and the second floor would be the public museum space.

Holak and Lorentz then pulled out their flashlights and invited me inside the mansion. We stopped first on the front porch and Holak pointed out the distinctive columns. With everything else falling down around, how do they stay up?

“They’re cast iron,” Holak said, and sure enough, I knocked on the two-story high columns and they “clanged” like an old kettle. Maybe this house, built in 1860 and listed as one of the city’s most “endangered” landmarks, might hold up after all.

But then we went inside.

I’ve been inside a lot of old and deteriorated properties, but this one was, well, the creepiest I’d ever seen. We walked a bit down the main hallway and glanced inside dark rooms filled with trash, crumbling walls and exposed wires. I’m not a haunted-house guy, but even this one seemed ripe for a ghost or two as a cold wind rattled through the old walls.

Holak and Lorentz were unfazed. They calmly pointed out the distinctive hardwood floors — “we can save that” — and some of the mouldings and architectural detail that were dirtied but salvageable. Lorentz flashed his light on an elevator shaft that he said would work. Holak said that conditions at Franklin School were just as bad, or worse, and talked about the rehab like any other home improvement project. He added that if financing gets approved, his company would start construction this spring or summer and it would be completed the summer of 2011. As he talked, I could almost imagine a warm and bright historic home filled with “active” seniors. Almost.

Ten minutes was about all I could handle in that place. After we shook hands, I walked to my car and glanced back at the building. I thought about all the people who had lived there — from the Clemens family to Roman Catholic nuns to Buddhist monks. But did Mark Twain? I don’t know, but it would have made a good story.

(Part II: History of the mansion’s inhabitants and the Mark Twain connection.)

Lindell Boulevard is one of the city’s best-known streets; it began around 1800 as a small path in the prairie leading to a spring near what is now Maryland and Euclid avenues. French colonials and others made their way from downtown to the spring to drink, gossip, quarrel and relax, according to CWE historian Mary Bartley in her book, St. Louis Lost. The street was named for Peter Lindell, a 19th century merchant who made his fortune in trade along the Ohio River and later as a holder of extensive real estate in the area.

Lindell Boulevard was the main street platted in the subdivision of the Lindell farm west of Grand Avenue. The subdivision of their farm into straight wide streets with large blocks was unique at a time when most additions were still conforming to the same old irregularities.

Later, in the early 20th century, city planner and architect George Kessler envisioned Lindell as one in a series of grand city boulevards that would connect parks, residential and business areas. In part, this plan was realized. During the World’s Fair of 1904, Lindell was an important route from the city to the fair; it’s westernmost section, from Kingshighway to Skinker, hosted an amusement park called the “Pike.” The grand mansions, institutions and apartment buildings that lined the street boasted some of the nation’s finest architects.

Fast-forward a hundred years. “Lindell seems schizophrenic,” said Carolyn Toft, former director of Landmarks Association. While some blocks retain their Victorian glory, many historic buildings are gone, including the Castleman-Mackay mansion at Spring and Lindell, now a parking lot for the next-door Masonic Temple.

The blocks east of Vandeventer to Sarah have been especially prone to change. A series of commercial buildings have been built and torn down from the old Windsor Hotel to the recent demolition of the San Luis apartments. Strip malls have been built and bland 1960s-style office buildings still stand.

Remember the Cinerama? This was a popular movie theater that I attended as a child. Built in 1962, it was billed as having one of the largest indoor screens in the world; 100 feet wide on a curve. I’ll never forget George C. Scott yelling and World War II army tanks marching across the screen during “Patton.” It’s at the site where the Walgreens now stands.

I do remember — but never visited, I promise — the old Playboy Club on Lindell near Vandeventer. It was Hugh Hefner’s fourth club, at 3914 Lindell. Also, the Windsor Hotel, built in the 1920s but torn down in 1993, occupied what is now the American Cancer Center Hope Lodge.

These blocks of jumbled urban architecture have been slowly upgraded with newer buildings which employ brick facades and architectural character lacking in the older ones. The Hope Lodge, the Walgreens, and yes, even the new McDonalds may not win awards, but they do blend better into the streetscape.

One new building which did win an award is the 3949 Lindell apartment building which opened this year. It’s a four-story, 200 unit structure which caters to students, staff and employees of nearby St. Louis University, Washington University and the Grand Center entertainment district. On Oct. 9, Mayor Francis Slay recognized the apartment complex as the city’s “Best Economic Project.

There’s still a long way to go to reduce the street’s “schizophrenia,” but perhaps someday Lindell will return to the grand urban boulevard that would make Peter Lindell proud.