In December 1942, Secretary of War Henry Stimson ordered the director of the remote Los Alamos Ranch School in northern New Mexico to shut down the elite school.

Stimson wrote in a letter that the land was being acquired by the U.S. government for “military purposes.” But school officials were forbidden from saying why the school closed on Feb. 8, 1943, and all records of the condemnation proceedings were sealed.

That was among many secrets that would soon shroud a town on the Pajarito Plateau about 35 miles northwest of Santa Fe.

The secretive history is one of the things that today draws people to Los Alamos, where the atomic bomb was developed and where Los Alamos National Laboratory continues to operate as one of the nation’s premier scientific laboratories. The town uses the cachet of “Secret City” and “Atomic City” in its efforts to attract tourists.

There’s plenty to fill a long weekend in Los Alamos and its surroundings alone, but if you pick one of two weekends each year, you can delve a little deeper into New Mexico’s atomic history by driving about 200 miles south.

For 7½ hours on the first Saturday in October and the first Saturday in April, the U.S. Army hosts an open house at Trinity Site, where the first atomic bomb was tested on July 16, 1945. You’ll find a few temporary information tables, about a dozen historical photographs hanging on the chain-link fence surrounding the site, a place to get a National Park passport stamp or souvenirs, a food truck and the requisite portable toilets.

You can stand in line for a selfie or group shot at the ground-zero obelisk (built in 1965) – and if you’re patient enough you might get a shot of it by itself.

There’s a shuttle bus to take visitors to the McDonald Ranch house, where the plutonium core of the bomb was assembled.

And that’s it.

The rest, as you stand in the barren desert and scan the distant mountains, is left to your imagination and your recall of the history of the Manhattan Project and the dawn of the Atomic Age. The nerdier historical aspect is what drew my daughter and myself to visit the site on April 7 and combine it with a visit to Los Alamos a day later for an “atomic New Mexico” tour. It was more pilgrimage than “bucket list” travel for us, a history teacher who has visited Hiroshima and a former reporter who for years covered the U.S. military.

Whatever the reason, it’s a worthy and scenic long-weekend trip from Durango that can be extended a day or two to include hiking or biking, local history and art museums and exquisite dining in Santa Fe.

The next opportunity to visit the Trinity Site is Oct. 6, when the Stallion Gate near Socorro, New Mexico, is open 8 a.m. to 2 p.m. for the open house. And it’s none too soon to reserve a hotel in Socorro (the nearest town) as they tend to fill up on open house weekends.

Our tripWe drove from Colorado Springs to Socorro on Friday, arriving in plenty of time to check into the hotel and relax a bit before dinner at the Sourdough Mine Restaurant, where we had a yummy plate of ribs and brews from New Mexico’s Sierra Blanca Brewing Co.

After reading all the information and watching videos on the Trinity Site website, we decided to head out around 9 a.m. to miss the anticipated backup at the gate when it opened at 8 a.m. I think 10 a.m. would’ve been better. The first 35 miles were a breeze, but then we hit the lane of cars inching forward to get through the gate. That took about an hour. Once through security, it was a smooth 15 to 20 minute drive to the parking lot.

You can also access the site with a caravan that makes a 145-mile round-trip from Tularosa, New Mexico, but you must be on their schedule.

Just remember, you’re on a military base, the Army’s White Sands Missile Range, and subject to all the rules that go with that. Our car registration and drivers’ licenses were checked, but that was it for us. They can search vehicles at will and weapons, alcohol and drugs are forbidden. All the details are on the website, so there’s no reason for surprises.

Two hours at the site was enough for plenty of contemplation time and a visit to the McDonald Ranch. The shuttles run routinely throughout the day so there’s little waiting.

It was unseasonably warm and dry that day with temperatures in the 80s. The Army advises visitors to come prepared for all kinds of weather, and we were glad for our water, hats and sunscreen, and the picnic cooler with refreshing fruit, veggies and cheese for the drive back out of the desert and north toward Los Alamos.

Shortly after leaving the base, we stopped to talk with protesters – “downwinders” – who had set up an information tent about the dangers the atomic testing had created for the community. They said that they always come out on open house days to provide their story to the visiting public.

We chose to spend Saturday night near Santa Fe, where there was more choice of hotels and restaurants. But we never made it to The Plaza, as we discovered Jambo Café in a strip mall not far from our hotel. The highly rated African restaurant deserves all the praise it gets online.

Los AlamosWe headed to Los Alamos early Sunday and arrived at the locally-operated Los Alamos History Museum as it opened at 9 a.m. We had time to see that museum, do the historic walking tour and have a picnic lunch at Ashley Pond before the Bradbury Science Museum opened at 1 p.m.

At the local museum, we learned more about what life was like in the Secret City, where for more than two years, no one could say anything about Los Alamos, known in the region as “The Hill.” People who worked there weren’t allowed to tell their family where they were, and many had no idea what super-secret project they were supporting. Mail was routed through a single post office box in Santa Fe and was heavily censored.

It was Project Y of the Manhattan Project, a military effort to design and build an atomic bomb before Germany did. Site X was the uranium processing plant at Oak Ridge, Tennessee, and Site W was the plutonium development plant at Hanford, Washington. The three sites today are part of the Manhattan Project National Historical Park.

The walking tour includes Bathtub Row, so named because they were the only houses that had bathtubs during the war years. They were inhabited by scientists, including Robert Oppenheimer.

Our final stop on the atomic tour was the Los Alamos National Laboratories’ Bradbury Science Museum, which offers detailed history of the Manhattan Project activity in Los Alamos, as well as displays about current research efforts in such areas as nanotechnology, biofuels and space science. There is even a small display dedicated to opposing views on continued development of weapons and their use, and a place for the public to write their thoughts about such scientific research.

Plenty to contemplate on the drive home, too.

Sue McMillin, a longtime journalist and former city editor at The Durango Herald, is a freelance writer and editor living in Victor, Colorado.