One of my favorite book series as a kid was The 39 Clues by several different authors (I can't imagine it's the only series to do so, but it's the only one I can think of that bounces from author to author between books like that).
For those not familiar with the premise, the series is about a pair of orphaned siblings who, upon the death of their rich and enigmatic grandmother, learn that they're part of a family that connects to every notable historical figure of the past few centuries. And through their grandmother's will, they're thrust into the midst of a globe spanning scavenger hunt, the prize of which promises to make the victor the most powerful person in the world.
I recently revisited the series and was happy to find that it still holds up quite well (and for a middle-grade series, I was surprised to see how unafraid it was to get dark in some spots. I imagine the respect it showed its audience is part of why I loved the series as a kid), and it got me wondering if there was anything quite like it that wasn't for a younger audience.
There are easy comparisons to be made to movies like National Treasure or The Da Vinci Code (which I know is also a book), but I think part of the series' identity is in the fact that it's a series. It being a longer form story gives a lot more room to explore both the characters and each location they visit. In that way you could compare it to the Tintin comics. Or, strangely enough, I think one of the closest feeling things to The 39 Clues that I've read is the mange JoJo's Bizarre Adventure (I'm not really sure if I can explain why, it just makes sense in my brain as someone who loves both).
I'm honestly having a bit of a hard time with identifying which aspects of the series I'm itching for more of. The globe-trotting adventure, mystery/thriller, and race/competition elements all compliment each other so well that it's hard to imagine that something could feel like it without any of those elements, but I also imagine a series that hits all those beats is an incredibly niche and specific ask. As far as I'm aware, the only thing that actually checks all those boxes is The 39 Clues. Hence the post. Of course, if you can't think of anything that magically fits perfectly, feel free to leave suggestions you think are close in spirit, a la my earlier comparisons of Da Vinci Code or Tintin.
by D-A_W