Here's a vanishing trick even David Copperfield would have trouble pulling off. Hide a century-old building that occupies an entire city block at a major intersection in the downtown core. On top of that, keep it hidden not just for a few minutes, or a day, but year after year.

There is no magic, of course, and yet even architecture buffs and preservation enthusiasts would have a hard time pointing you toward the Federal Office Building in downtown Minneapolis. Quietly occupying the bustling intersection of 3rd and Washington Avenues S. since 1915, the low-slung mass of gray granite is a top contestant for the Twin Cities' most overlooked landmark.

While the storybook clock tower of the Milwaukee Road Depot just across the street grabs focus from tourists and commuters alike, the Federal Office Building has just as rich a history, and just as pure an architectural pedigree as any antique edifice in the city. Just a few months shy of its hundred-year anniversary and with substantial renovation work underway or recently completed, the Federal Office Building merits renewed attention.

Originally designed as the Minneapolis main post office, it served that role only briefly. Mail operations were moved to the extant WPA Moderne Main Post Office overlooking St. Anthony Falls in 1936. A light renovation converted the building for office use by a patchwork succession of branch bureaucracies. Since then, its life as a public structure was more or less over.

Listed on the National Register of Historic Places in 2010, it is one of a few remaining neoclassical revival structures in the central business district. The building racks up high marks for style compliance — classical details copied from ancient Rome, a highly symmetrical design, monumental entry stairs and vaulted public lobbies and hallways. Largely a one-story structure, the side facing 3rd Avenue S. is graced with a double-height colonnade of paired Corinthian columns supporting a richly decorated entablature.

Supervising architect James Knox Taylor, who oversaw thousands of federal building designs each year through his office at the U.S. Treasury, dictated the neoclassical design. Taylor, like many architects and city planners of the period, was hugely influenced by the World Columbian Exposition held in Chicago in 1892-93. So was his boss, Lyman Gage, the William McKinley-appointed secretary of the U.S. Treasury and former president of the Columbian Exposition board.

Spurring the popularly named City Beautiful movement, the exposition captured the public imagination as the architectural image of an American republic. Architects for large public buildings were eager to sign on for the dream. The neoclassical style dominated public buildings through the early 20th century.

Although an architectural wallflower, the Federal Office Building shares DNA with its more outgoing neoclassical siblings — the Duluth Civic Center (1908), Union Depot in St. Paul (1917-26), the Minneapolis Institute of Arts (1915) and the Mall of the University of Minnesota (1908).

The gleam of the City Beautiful movement, however, could not protect the Federal Office Building from later abuses. It survived the great urban renewal razing of the adjacent Gateway District in the early 1960s largely because the owners, the feds, were the ones doling out the demolition money.

Later, in 1970, Vietnam War protesters blew up the north entry when the building housed the offices for the Selective Service, requiring $500,000 worth of Nixon-era repairs. In more recent years, the government tenants fled the worn-down hulk, the vacancy rate approaching 75 percent.

Thankfully, the General Services Administration stepped up its game to ensure that the building remains viable into the future. Today, you can go to the Federal Office Building to renew your passport, passing through a newly updated lobby and security station. The design work was a collaboration of A-list Twin Cities firms — Snow Kreilich Architects, MSR, HGA and the Collaborative Design Group. The high-quality renovation merited a local Heritage Preservation Award this year.

Not surprisingly, when the award was announced, more than one architectural insider was heard asking, "Hey, where is that anyway?"

Phillip Koski is an architect and writer.