William Penn is finally getting his Centre Square back. Or, at least how he might have envisioned it 400 years on.

In this reimagining, there will be ice skating, programmable fountains, an upscale cafe, well-lit access to subways, and open space - lovely, inviting open space, all on the doorstep of City Hall.

"We envision this as the center of our city, the center of our neighborhoods," said Paul Levy, chief executive of the Center City District (CCD).

On Sept. 4, what was Dilworth Plaza, an off-putting, at times even threatening, hardscaped remnant of the well-intentioned but often misguided 1970s, is to reopen as Dilworth Park, a softer, greener, refurbished front porch for Philadelphia's civic hub.

Three days of music, feasting, and general merriment will follow as the city looks to introduce the $55 million remake to the public.

The project is a bit behind schedule. By Sept. 4, about two-thirds of the park's surface area, on the western apron of City Hall, will be completed. The remainder is to be opened by Thanksgiving.

Fully finished and accessible by Sept. 4 will be the new transit concourse and connections to the Broad Street subway, the Market-Frankford El, and the Regional Rail system.

"We are positioning this as the gateway to the sports complex, as the gateway to West and North Philadelphia," Levy said, "to Temple University and the regional transit system."

The project has been headed by the CCD, which contributed $15 million to the $55 million overall cost. Other major contributors are the city ($5.75 million), the state ($16.35 million), the Federal Transit Administration ($15 million), and SEPTA ($4.3 million). The William Penn Foundation provided $1.2 million. The design and construction team included KieranTimberlake, Olin, Urban Engineers, Gilbane Building Co., and Daniel J. Keating Co.

Construction began in January 2012, not long after the Occupy Philadelphia protesters and their tents were rousted from the site after two months.

The project was scheduled to be completed by spring of this year, but ran into several snags - not the least being the discovery of long-buried foundations, stairwells, pipes, conduits, and duct banks from the site's previous incarnations.

"We hit some serious unforeseen conditions underground," Levy said Tuesday at a briefing for reporters. He said the impediments had added $5 million to the project's initial $50 million budget.

This past winter's extreme weather did no favors, either, causing five to six more weeks of delay, he said.

Still another reason it has taken this long: The fact that the project was more complicated than it might have seemed from street level, Levy said. Two underground levels, vast expanses totaling 40,000 square feet, had to be completely reconstructed to make the intended improvements to transit access, he said.

Chief among those improvements was replacing the meandering underground maze that connected various transit lines. Instead there will be a single, brightly lit walkway.

"I liked to say that if you gave an architect the challenge to design a dangerous space, that is what they would have created," Levy said of the old concourse.

Above ground, the park will be unlike the old plaza in myriad ways, including having none of the previous impediments to movement, such as shifting levels and granite walls. Rather, it will be a sweeping, graded space with lawn and trees, and a pair of arcing glass headhouses - entrances, that is - leading underground.

At the north end of the park will be a cafe, Rosa Blanca, operated by Jose Garces. In winter, its fountain field, with recessed jets, will become an ice-skating rink. There will be room for weddings, concerts, parties, and all manner of get-togethers.

All told, the park will vastly remake a key element of central Philadelphia, restoring it closer to Penn's original vision. The founder intended that location as the central hub of five public spaces, augmenting what are now Washington, Rittenhouse, Logan, and Franklin Squares.

Over the centuries, it was home to the city's first waterworks, its first public fountain, and its seat of government. Levy hopes it will be more again - "a central gathering place. The original 'Centre Square' as William Penn designed it to be."