PHILADELPHIA - Ever walk by a statue and wonder, "What made this guy so important?" or pass by a modern sculpture in a park and think, "What on earth is that supposed to be?"

Now, in Philadelphia, there's an app for that. And similar apps exist for art and landmarks in other cities ranging from Seattle to New York.

In Philadelphia, the month-old "Museum Without Walls" audio program was created to be used like a customizable museum that's free and never closes. Its self-guided audio tours are available 24-7 in several formats: You can call phone numbers listed with each sculpture, use a free smart phone app, download the audio at to an MP3 player, or scan a special bar code (known as a QR or quick response code) on the free "Museum Without Walls" map at locations around the city.

The project's first phase includes 51 outdoor sculptures at 35 stops along a three-mile stretch of the bustling Benjamin Franklin Parkway from downtown to leafy Fairmount Park, a route popular with bicyclists, runners and walkers.

The first stop is Robert Indiana's iconic "LOVE" sculpture. Others along the way include Auguste Rodin's "The Thinker" and Emmanuel Fremiet's "Joan of Arc," plus works by Henry Moore, Mark di Suvero, Alexander Calder and Augustus Saint-Gaudens.

Three- to-five minute segments voiced by people connected to the works - historians, curators, the artist himself (they're all men so far) or a living relative - explain each piece and give context. On the website, visitors can upload their own pictures and add their thoughts about the sculptures.

Indiana, for example, explains how his early years as a newspaper copy boy sparked his interest in the typography that became a recurring theme in his work. In each case, the segments sound like a conversation instead of a lecture.

City resident Ann Sebatino plugged into the Indiana podcast during her lunch hour and gave it high marks: "You get a lot of cool information in just a couple of minutes."

"Our main goal was to make the content really great," said Penny Balkin Bach of the Fairmount Park Art Association, a 128-year-old nonprofit that acquires, interprets and maintains more than 200 works of art citywide. "Technology is always changing ... the important thing is what you find after you've dialed the number."

Museum Without Walls, which was funded by grants, is geared toward tourists as well as locals who have always wondered about particular works of art - or barely noticed them at all. Another 35 sculptures may be added next year if grant funding comes through, Bach said.

Meanwhile, several museums around the country are using the Philadelphia program as a model.

"The excellent quality of the recordings and innovative use of multiple media in the Museum Without Walls make it a valuable model to learn from," said Kyrie Thompson Kellett of the Oregon Museum of Science and Industry.

The Getty Museum in Los Angeles offers similar technology to visitors of its outdoor sculpture garden, and Seattle has a virtual tour of historic landmarks. But perhaps the largest such program is in New York City.

After the World Trade Center attacks on Sept. 11, 2001, a group of architects and planners began an endeavor to document the art and architecture of lower Manhattan. That developed into a nonprofit called CultureNOW, which has since created five different maps, a website and a $1.99 iPhone app that includes 200 podcasts narrated by the city's movers and shakers.

Abby Suckle, an architect and the president of CultureNOW, calls the survey the most comprehensive to date of New York's cultural landscape, including 2,000 public art works, plus thousands more in museums, galleries, historic buildings, theaters and parks.

"All of it is online and all of it is documented," Suckle said, from art in public schools and subways to grand public spaces such as Rockefeller Center and the United Nations.