The secret to winning the U.S. Open?

ARDMORE, Pa. – Before he won the PGA Championship at Baltusrol in 2005, Phil Mickelson played there. Before he won the U.S. Open at Congressional in 2011, Rory McIlroy played there. And on Tuesday, another major winner played there in preparation for the 113th U.S. Open, which kicks off Thursday.

"There" is Pine Valley Golf Club, home to an 18-hole track most of America has never seen on TV or, perhaps, never even heard of. It's never hosted a major. In fact, it's hardly ever hosted a tournament. Yet over most of the last 30 years, Golf Digest, which has been in the rankings business for a half-century, has ranked it the No. 1 course in the United States.

Not Augusta National. Not Pebble Beach. Not Shinnecock Hills. Not Winged Foot.

It's Pine Valley Golf Club, only 20 minutes from Philadelphia – 30 from Merion Golf Club, site of this week's U. S. Open – and it's been a little bit of a good luck charm for some of the top players in the world.

"We've had an interesting group of people play here before they won major tournaments," says Pine Valley's general manager, Charley Raudenbush.

No wonder, when you consider any other course is (arguably) a step down from Pine Valley. Even Merion, historic and beloved, ranks No. 6 on the Golf Digest list. Pine Valley, located just across the border in New Jersey, was the No. 1 course in the world from 1985 to 2000, then from 2003-08, and again this year after losing the spot to Augusta National.

So why hasn't Pine Valley ever hosted a U.S. Open?

"The facility isn't conducive to it," says Raudenbush. "We have a small clubhouse. We don't have room for spectators."

The course doesn't have much room for anyone. There are only 125 rounds or so played there on a busy day. (On Wednesday, that included five former U.S. Open champions.) Babe Ruth has played there. Michael Jordan has played there. Women are allowed to play only on Sundays. Invitations are as rare as winning lottery tickets, as there are only 1,000 members and their identities are kept mostly secret. The public is allowed on the grounds only one day per year.

"I've played over 750 courses in my life," New York Daily News writer Hank Gola told the Star-Ledger (N.J.). "It was one of the greatest days of my life."

To golf experts, Pine Valley has the best of everything: a blend of European flavor and American roots. Holes don't run parallel to each other, so each fairway is a world of its own – hideaways within a hideaway. The bunkers are not raked. "Robert Trent Jones felt it had more classic holes than any other," writes Golf Digest, "and regarded it as the first course that truly tested every club in the bag." Pine Valley has the highest possible slope rating (golf's degree of difficulty) at 155.

So while Merion becomes even more famous this week, at least in the public eye, its top-ranked neighbor across the state line will continue to revel in privacy. It's even difficult to find – "Behind an amusement park and nestled between two towns," Raudenbush says. One of the entrances is hidden, almost like a secret passageway.

So who's the famous pro who has made the trek from Merion to Pine Valley this week to play a round? Raudenbush, true to form, would rather not reveal his identity. It's not Tiger Woods, who has been invited but hasn't played there yet. But it is someone who has won a major fairly recently.

Perhaps he'll talk about it if he wins. But probably not. Like most other aspects of the best golf course in America, this sliver of Pine Valley lore will likely remain far away from public view.

Related coverage on Yahoo! Sports:
Inside Tiger Woods' five-year majors drought
Merion a step back in time for U.S. Open
Phil Mickelson's recent surge puts him in U.S. Open discussion