Mammoth sphinxes guard the House of the Temple of the Scottish Rite, a formidable neo-Classical building in the heart of Washington, D.C. Inside, Egyptian hieroglyphics adorn a soaring atrium. The building's nine-foot-thick walls hold human remains. Bronze coiling snakes flank a large wooden throne, canopied in purple velvet, in a second-floor inner sanctum called the Temple Room, where men from around the world gather behind closed doors every two years. Over the centuries the select membership has included signers of the Declaration of Independence; George Washington, Theodore Roosevelt, Gerald Ford and 13 other presidents; Senators Charles Schumer and Robert Dole; Chief Justice Earl Warren and other Supreme Court justices. Formally they are known as Freemasons, but most people know them simply as Masons. And this artfully forbidding edifice, a mile from the White House, is their southern headquarters. Long viewed by outsiders as a mysterious society and one of the world's most powerful fraternities, Masons have recently become the object of even more curiosity as filmmakers and novelists mine Masonic legends and symbols for the stuff of conspiracy. In the 2004 thriller National Treasure, Nicolas Cage followed Masonic clues and invisible writing on the Declaration of Independence in search of a hidden cache of gold. Dan Brown, author of The Da Vinci Code, has said his next novel would involve Masonic architecture in Washington, D.C. His Web site challenges readers to find Masonic clues on the dust jacket of The Da Vinci Code. Perhaps because of such intrigue, the number of visitors to the temple has tripled over the past two years to 12,000. Which shows that Masons have nothing to hide, says retired Maj. Gen. Armen Garabedian, a Mason for 49 years. "This secret thing stems from way back," he says. "If we were a secret organization, tours would not be offered." The temple has always been open to the public.