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For as secretive as the National Security Agency can be—it’s jokingly been referred to as “No Such Agency” or “Never Say Anything”—it hides in plain sight just north of D.C. Unlike its better-known clandestine counterpart in Langley, you can drive right up to the NSA’s entrance; it isn’t more than a quick exit off of Route 32 in Fort Meade, itself a quick exit off of the Baltimore-Washington Parkway.

That’s where I found myself last week, staring at the iconic—if boxy and unremarkable—glass-enclosed buildings that house a large part of the agency’s 40,000 employees. In the wake of former NSA contractor Edward Snowden’s dramatic disclosures about the agency’s massive electronic eavesdropping capabilities, it seemed surreal to look up at the pair of buildings where federal employees are tasked with digging through mounds of electronic detritus—phone logs, emails, Facebook posts, and who knows what else—to trace and disrupt the next possible terrorist attack.

But while the agency’s headquarters invokes an aura of imposing secrecy and security-minded ruthlessness, a single-story building around the corner has for two decades tried to do just the opposite: demystify what the NSA does and describe the many ways its work has had a consequential impact on the country.

Housed in what was once a cheap motel, the National Cryptologic Museum is the agency’s modest attempt to document its raison d’etre. A virtual Smithsonian of spycraft, the museum was founded in 1993 at the prodding of NSA employees who had collected and displayed the tools of their trade—cryptology, the practice of making and breaking codes—in the agency’s headquarters.

“The museum exists to educate the public about the field of cryptology, key people in our history who accomplished great things, and the machines, devices, and techniques they developed,” says Louis Leto, an NSA spokesman, probably relieved to be dealing with questions about tourism, not telecommunications intercepts.

The museum’s exhibits both explain the mechanics of cryptology and put its practice in historical context. Making and breaking codes played a vital role in just about every conflict the U.S. has engaged in, from the Revolutionary War to World War II and beyond; American victories in those wars largely came from knowing what the enemy planned to do and preventing them from knowing what the U.S. would do.

The artifacts on display range from an 18th century cipher thought to have been owned by Thomas Jefferson to the Enigma, a mid-20th century cipher typewriter that the Germans believed could produce unbreakable codes. (They were wrong.) There’s also a first-generation Cray supercomputer, which was used from 1983 to 1993 and revolutionized the NSA’s ability to store, process, interpret, and decode vast amounts of information. Newer versions of those same supercomputers—though significantly faster—power the very surveillance programs in the news today, sweeping up millions of emails, phone calls, and other electronic data and helping the agency make sense of them.

The museum’s detail-rich exhibits are spread out through a few rooms; there’s a small library, and yes, even a gift shop with a limited supply of NSA-themed apparel—T-shirts, hats, and shot glasses. In showing that spycraft and subterfuge are a family affair, the museum tailors its content for kids—“CryptoKids,” as they’re called—by letting them break simple codes associated with specific exhibits. There are even NSA-approved mascots, among them Crypto Cat (“She loves to create secret messages to purr-plex her friends”) and Decipher Dog.

The museum conveys a simple message, similar to the one NSA director Keith Alexander and Director of National Intelligence James Clapper have been trying to push since the details of the agency’s PRISM program came to light: Knowing what their enemies are saying has enabled the good guys in history to prevail over the bad. More than that, though, the National Cryptologic Museum is a memorial of sorts, a public recognition of the work done by legions of cryptologists who toiled in state-mandated anonymity.

“To commemorate the men and women of American cryptology, uniformed and civilian, who, unknown to the public, and often their families, served their country and the free world, constituting what is truly America’s silent service,” reads a plaque installed at the museum’s opening two decades ago.

Of course, secrecy is a habit that’s hard to break. When the museum threw open its doors to the public in December 1993, there weren’t many people on hand to bear witness. The publicity-averse NSA hadn’t even bothered to tell anyone about the museum, the story goes, and it wasn’t until January 1994 that the Washington Post broke the news of the museum’s existence. Since then, though, some 50,000 to 60,000 visitors have passed through the museum’s doors annually. (Admission is free.) That’s only a fraction of what many Smithsonian museums see; the National Postal Museum got 321,963 visitors in 2012. It’s about 10 percent of the visitors the private International Spy Museum gets downtown, but the mélange of people that travel out to Fort Meade speaks to the museum’s scrappy appeal.

“The NSA is in the media right now, not necessarily for good things, but nevertheless that put it in the front of my mind,” says Chris Martinka, an emergency medical technician from Northern Virginia who was roaming the museum earlier this week. “I’ve heard that where the Spy Museum is geared toward entertainment, while this is geared toward documentation and history.”

As one of only two official intelligence museums in the country (the other is the U.S. Army Intelligence Museum at Fort Huachuca, Ariz.; the CIA has a museum, but it’s not open to the public) the National Cryptologic Museum is a fascinating attempt by an agency that would rather the public not know it exists to explain exactly why it does exist—and why it should matter to you. (The museum doesn’t represent NSA’s first venture into cultural affairs. In the 1950s and ’60s, the agency hosted a yearly Miss NSA pageant. Little is known about the pageant; the only public evidence of its existence seems to be a historical photo from the NSA’s formerly secret archives.) It’s also evidence that people who do secret work often want to tell their story; one docent, I was told, worked at the NSA for 50 years before retiring in 1994. He now leads free tours of the museum, no security clearance required.

But like any official recounting of history, the museum sticks to a pretty black and white, good-versus-bad portrayal of the agency’s mission over its 60-year existence. That makes some sense—past conflicts were fought between uniformed soldiers according to age-old rules of war, and it’s unquestionable now that the world is a better place because the U.S. was able to defeat Germany and Japan in World War II.

Things have gotten much murkier since, and the museum only gives passing reference to how the NSA’s mission changed post-9/11. While breaking codes passed between government officials of enemy powers may have been the norm when the NSA came into existence, it now finds itself having to cast a much broader electronic net to fish out stateless terrorists who use the same means of communication as the people they want to kill. As Snowden’s leaks have evidenced, that net is shockingly wide.

That, of course, raises the question: Will we see Snowden’s exploits touched on at the museum? Like a good spy, Leto, the agency spokesman, demurs: “We can’t at this point anticipate a future exhibit on this.”

Graphic by Carey Jordan