Many people in Philadelphia don't know that there's a park at Penn's Landing Marina, hugging the Delaware River between Spruce and Dock Streets - and they definitely don't make a point of going there.

That may change June 27 with the opening of Spruce Street Harbor Park, the most ambitious and expensive pop-up yet to transform a forgotten Philadelphia space into a destination.

With three barges holding a floating restaurant and giant hammocks cantilevered over the water - plus mini art galleries, a water garden, a walkway of misting arches, and a slew of places to play games, buy snacks, or nap in a lounge chair - it will cost upward of $700,000.

The Delaware River Waterfront Corp. (DRWC) is staging this spectacle with hopes that pop-ups - starting with the Waterfront Winterfest it set up at the Blue Cross RiverRink in November - just may be able to do what, so far, nothing else has: drive major investment to this part of the waterfront.

"If we can demonstrate that 75,000 people will come to this park . . . if we can start to position this park as a real asset, then we can spark development interest in this area," said Jodie Milkman, director of communications and programming for the DRWC. A $310,000 ArtPlace grant for "creative placemaking" helps fund the project.

"The overall return in private development would bring back [manyfold] the public investment, should all the pieces come together," she said.

DRWC is betting it can educate visitors about what the waterfront has to offer, showcase the area as a year-round destination, and overcome a development history rife with false starts. One short-term goal is to attract developers for the three acres of real estate by the marina. The waterfront master plan calls for mixed-use low-rise construction, though the DRWC still intends to do engineering, planning, and market studies before putting out a request for development proposals there.

DRWC director of operations Joe Forkin points to Morgan's Pier and FringeArts' headquarters and performance space - plus other proposed developments along Race Street and Columbus Boulevard - as signs that public investments in a slick park built at Race Street Pier in 2011 and an upgraded underpass connecting pedestrians to the site already have paid off.

But further verifiable signs of life have been elusive. A high-rise at Second and Race Streets, after a public zoning fight a year ago, hasn't broken ground; the Marina View Tower, which was approved in 2012 for a site near the Ben Franklin Bridge, hasn't materialized; and a scheme for more than a thousand apartments at Columbus Boulevard and Callowhill Street is so far just a rendering.

Still, given that there are limited public dollars, pop-ups represent an opportunity for instant gratification at lower cost.

That may help explain why Philly has become rather pop-up happy in recent summers.

This year, there will be at least two other major temporary parks, with varied goals: The Oval, the city's $224,000 effort to revitalize the Benjamin Franklin Parkway in between festivals and road races, is open again this spring. It drew 30,000 visitors and enough revenue to more than break even last year. The Pennsylvania Horticultural Society, which in 2013 attracted 30,000 visitors to a vacant lot on South Broad Street near Spruce that was transformed on a shoestring into a woodland retreat/beer garden, also is planning its next takeover.

While the DRWC's project costs far more than either of those, much of that money represents a long-term investment in the short-lived parks.

Capital investments for shipping containers, trees, and lighting were used for Winterfest and will be deployed again in future iterations of Spruce Street Harbor Park - or whatever pop-up DRWC dreams up next. Other improvements could remain after the pop-up closes on Labor Day - like the restoration of two long-decommissioned fountains.

Design firms Digsau and Interface Studio collaborated on the design with Groundswell Design Group, which also created the DRWC's Winterfest configuration, which drew record crowds to the RiverRink site this winter despite 13 days of weather closures.

Groundswell's David Fierabend is optimistic that incremental improvements on the waterfront can add up.

"There's more awareness, because you're adding levels to it," he said. "You start with Race Street Pier, and then you add Morgan's Pier and Winterfest and FringeArts. There starts to be an energy that builds. I think perceptions are definitely changing."