We were standing in the gift shop of the Badlands National Park visitor center when my husband picked up a little blue book and asked me if we should get one. “My sister has one and she says that it’s a cool way to keep track of all of the places that you visit.”

I looked at him. Like most early 20-something Xennials, we were just starting in our careers, irresponsibly living at or above our means, and we had no idea what the future held. Impulsively spending money on a silly little blue book just seemed unnecessary. “Besides,” I responded. “How many more national parks do you really think we’re going to visit over our lifetime?”

I said those words near the beginning of a week-long trip that included stops at Badlands National Park, Mount Rushmore, and Yellowstone National Park (we inexplicably drove right past the Grand Tetons). Those words would come back to haunt me when, two years later, we were standing in the gift shop at yet another national park, this time Mammoth Cave in Kentucky, purchasing our little blue passport so that we could put a dated park stamp at the beginning of the Southeast region of the book. I pulled out the map and for the first time really considered what each of those little dots could represent. We dreamed of someday returning to Yellowstone with our yet-to-be-born children. We had several places we wanted to visit that were near national parks and historic sites. We were two adventure-seeking, history-loving, camping enthusiasts. Having a book that would both show us where we could visit and give us a way to track it just seemed natural.

The book has traveled around the country and has become a minor obsession of mine (but if you asked my husband he would probably say it is more like a major obsession and he occasionally regrets ever making the suggestion in the first place). When we went to Washington, D.C. so that I could attend a conference, we hopped on our bikes during our last day in the city and zipped from one monument to the next, getting a stamp at every single one except the Washington Monument since we weren’t able to take the trip to the top. On the way home from that trip we stopped in Philadelphia and stamped our book at all of the locations in Independence National Historical Park and then drove the short distance to the Edgar Allan Poe National Historic Site for a bonus stamp. The next day, as we headed home towards Indianapolis, we stopped at Valley Forge and then raced against the clock to make it to the Gettysburg visitor center before it closed so we could get two more in one full day of driving.

Then we had kids. When our kids were just three and one we bought them their own books while we were in the Great Smoky Mountains for a family reunion. It was just the beginning of their stamp collection, which now stretches across the Midwest and part of the South. More than the Junior Ranger pins that they have started saving on their vests, their books are a record of the places they have seen. A couple years ago, when the three of us drove back home to Houston from Indianapolis (my husband had to fly home early), we made special stops at Abraham Lincoln’s home in Springfield, Illinois and, after an overnight stay with friends in St. Louis, we made it to the national historic site at Central High School in Little Rock with 45 minutes to spare, allowing us to not only get stamps but also learn and explore at the visitor center.

That’s not to say that this quest for stamps has always ended smoothly. To this day my husband will not let me forget the trip the two of us took to Gettysburg without the kids and with our brand “new” camper. It was his first time ever towing a camper, we were driving through the Ohio hills, and I had seen that there was a potential stamp stop in Cuyahoga Valley National Park. Unfortunately, the directions to the hard-to-reach visitor center were complicated and not easy to navigate with an extra 20 feet hanging off of the back end of our truck, and we finally gave up and kept traveling to our reserved camp site. Needless to say, the tension in the truck hung over us until after we arrived at our overnight destination and we had set up camp for the very first time. Despite the other amazing stops at the Johnstown Flood Memorial, the Flight 93 Memorial, and the battlefields of the Gettysburg Military Park, he doesn’t hesitate to bring up that particular incident when I start to suggest making an out-of-the-way stop so that we can get just one more stamp.

I may have inadvertently passed along this desire for more stamps to our adventure-seeking children who can be bribed with the possibility of making a national parks stop. Unfortunately, that can also sometimes backfire on me.

Shortly after we moved to Texas and got our second dog, our son walked into the living room to discover that one of the dogs had gotten a hold of his passport book, tearing it to shreds. I had to reassure our devastated little boy that 1) we would get him a new book and 2) I would cut out all of his stamps and glue them into his new book. Those plans were nearly thwarted by heavy spring rains that prevented us from our original camping plans in Louisiana, but even though we had to camp in Texas, we still made it to Cane River Creole National Historic Park where he purchased a brand new book, complete with the centennial insignia on the front cover. He was able to join the rest of the family in stamping books and recording the date of our park visit.

However, my promises of stamp stops don’t always work out so smoothly. Last Thanksgiving I had every intention of making it to the Jazz National Historic Park in New Orleans but I didn’t pay attention to the signs and directions that clearly marked the new location along the riverfront, not the old location in Louis Armstrong Park. While our family had an enjoyable walk to and around the statue filled park, we didn’t make it to the actual NPS park until well after close. I didn’t do a very good job of masking my disappointment and our son declared that we were going to have to return to New Orleans someday, just so that we could get those stamps; I secretly agreed.

Then there were the thwarted Christmas break plans. We had made reservations in the Davis Mountains so that we could visit Fort Davis National Historic Site and additional reservations just outside of Big Bend National Park so we could also explore there. Despite the government shutdown, we continued with our plans to head to western Texas and while I had a difficult time accepting that I wouldn’t be able to use any of the stamps that sat behind locked doors at Fort Davis and in Big Bend, I was thankful that my husband had talked me away from the ledge and convinced me that the vacation would still be worth it. And it absolutely was.

Even with the mishaps, that little book has been the guide of many an adventure for the last thirteen years, and now our kids are joining in the fun. And while there is something satisfying about marking off another spot and recording it for future memories, there’s more to it. The more we’ve used the book, the more we have sought the opportunity to see more of our country and experience everything that the National Park Service has to offer. It has gotten us into nature, exposed us to the more interesting and darker sides of our nation’s history, and has shown us the uniqueness of each region of our vast country. It’s become more than a souvenir; it’s been a key unlocking a world of possibilities. And that has made our little purchase 100% worth it.