Ballyhooed as the “largest retail development in San Francisco” since the Westfield Centre, the 6x6 center, located at 900 Market between Sixth and Fifth Streets, anticipated becoming a major competitor in the retail scene.

Today the 250,000-square-foot, glass-and-steel behemoth remains vacant, with neither retail nor dining in sight, and only an underground parking structure as its sole revenue generator.

What happened?

For starters, brick-and-mortar retail is struggling. With department stores in Union Square closing each year (some of them turning into spaces for Instagram selfies), it’s hard to find eager retailers willing to sign anything in the area much less inside the Mid-Market 6x6 complex.

Earlier this year, developer Cypress Equities filed an application to convert two floors inside the complex into office use, effectively cutting retail space from 264,000 to 216,000 square feet.

“Planners supported that conversion because the office space was on upper floors and is well-served by existing and future public transit options,” reported San Francisco Business Times in August.

Speaking off the record, a source with 6x6 explained, “There are currently no tenants, but lots of leasing activity” and “the building is staffed, but there are no occupancies.”

However, “two major occupants” should be revealed by year’s end.

But for a structure of this size in a seemingly prime location, it does give pause for concern. After all, the current median ask per square foot for commercial space in the area is $68.76. Hardly chump change.

Buildings like 222 Sutter, once home to a Loehmann’s department store, which remains vacant, and the Macy’s Men's Store property in Union Square, sold to Morgan Stanley for $275 million, provide enough evidence that retail remain in peril.