Krista Yutzy-Burkey remembers how her hands shook last year when she and her husband, Steve, signed the contract to buy a century-old public bathhouse at Front and Girard in Fishtown. With its dramatic arched entrance and soaring interior, the building was perfect for their new business, an arts-focused children's play space. The location, not so much.

The bathhouse sits in the lee of the Market-Frankford El, the elevated train line that courses down the middle of Front Street, through the millennial precincts of Fishtown and Kensington on its way to the Frankford Transportation Center. Yet, even as the rowhouse blocks on either side began making a comeback in recent years, the murky, blighted strip under the El remained a notorious haven for drugs and crime - the last place a parent would want to push a stroller.

There were so few pedestrians on Front Street that "people would confuse me for a prostitute," says Shanta Schachter, deputy director of the New Kensington Community Development Corp. Frankford Avenue, the parallel main street two blocks east, is where all the hip restaurants and shops went.

But Front Street has unexpectedly stepped out of the shadows.

It started slowly, with the construction of Kensington CAPA in 2010 and the Oxford Mills apartments in 2013. "Eighteen months ago, the street was very iffy," says Yutzy-Burkey. "It's a completely different place today." Last week's preopening party for her learning center, PlayArts, drew 160 people.

As she and her husband cleared debris from the bathhouse and reconstructed the interior with the help of architect Jeremy Avellino, they noticed that other property owners were doing the same. New houses, restaurants, and offices started appearing amid the vacant lots. The trickle of millennials from the El stations at Girard, Berks, and York-Dauphin swelled to a torrent.

Philadelphia, of course, is full of similar warp-speed neighborhood transformations. But is there any turnaround as improbable as Front Street?

Since its completion in 1922, the Frankford El has been a blessing and curse for the northeastern neighborhoods. It whisks residents to the job clusters of Center City and University City in minutes, yet the relentless, ear-numbing rumble of the trains has made the houses below virtually uninhabitable. Every time a train rolls through, sidewalk conversations stop.

That annoyance no longer seems to matter, so great is the hunger for buildable lots in Fishtown and the many emerging subsets of Kensington - South, East, Somerset, Old Richmond. In defiance of the laws of physics and real estate, the homey Front Street Cafe set up shop last year on the corner of Thompson Street, a few steps from the El. This spring, a high-end Italian restaurant did it one better: After embedding itself in the shell of the former Wm. Mulherin's Sons whiskey merchant, the owners put out sidewalk tables. Even with that extra seating, reservations are still hard to come by.

The noise and perennial gloom no longer seem to function as a deterrent for Front Street. Developer Roland Kassis, who played a big role in Frankford Avenue's revival, says he plans two outdoor dining spots, including one that will host a Lebanese-theme food market. Farther north, at Norris Street, the Five Sisters dessert cafe has set up a garden with picnic tables. An Indian restaurant does a brisk business nearby.

It's not just restaurants that are reclaiming Front Street. Honeygrow, the fast-casual restaurant chain, moved its corporate headquarters to an industrial building at Oxford Street in the spring. After preservationist Oscar Beisert helped save a crumbling, 19th-century Presbyterian church, Kassis bought it and will give it new life as offices. Architect Richard Stokes, who was responsible for the interiors at Mulherin's, is designing that space as well as a City Fitness gym in a former factory. It opens in November.

With its wooden roof trusses and skylights, that lofty interior is a virtual carbon copy of the Frankford Avenue building that houses La Colombe. It turns out that part of Front Street's appeal is the eclectic mix of spaces that predate the El, some industrial, some civic, some residential. Architect Brian Phillips sees its authenticity as the allure, "gritty and scary, but also a little bit awesome."

Phillips' firm, ISA, is responsible for designing the stretch's most interesting new building, a six-unit apartment house that he dubs "El Chalet." Wedged between a vacant lot and a garage, its design is informed by both the extreme site conditions and the zoning requirements. Though it made sense to keep the apartments as far back from the El as possible, the zoning requires the front of the building to match the dimensions of a three-story rowhouse.

After creating what is essentially a false front, Phillips gave the rest of the building the sloping profile of a Tyrolean mountain. The false front acts as a sound barrier for the balconies facing the El. And, in a witty bit of architectural play, Phillips and developer Peter Crawford had a street artist paint the word Elevation on the north wall, calling out "El" in blue letters. But elevation is also the architectural term for facade, as well as a common way to describe a mountain slope. It's just too bad the integrity of the south facade is marred by the clunky air conditioner units.

Generally speaking, rowhouses are a poor use for Front Street, where older homes are holding on by a thread. Yet, because land is still cheap, developers have been scooping up parcels and inserting ticky-tacky rowhouses. It's not clear how these buildings will fare, especially with noise and environmental issues.

This disposable approach to architecture is a far cry from the thoughtfulness lavished on the old bathhouse, which has survived intact since 1907. Avellino's firm, Bright Common, renovated the building using nontoxic, energy-efficient materials and plenty of scavenged wood. Mahogany-framed windows were custom-made to keep out noise and fit the graceful, arched openings.

Steve Yutzy-Burkey, a carpenter, built all the wooden play equipment, which was tested by their 4-year-old son, Milo. Many of the interactive play stations are designed to evoke familiar neighborhood sights, like the milk bottle tower on top of the old Harbisons' dairy, and a rowhouse-shape playhouse. Front Street may be coming back, but the elements are a reminder that the gritty world of the El is just outside the door.