An adventure is more of a "personal growth" story; there is not necessarily a mystery to solve that motivates the story. In the TV Series Farscape, an astronaut is flung across the Universe, and must learn to survive there.
He did have an ultimate goal, to eventually find his way back home, but a goal is not a "mystery". The adventure was the point. His learning to fit in, to be valuable, to make friends and lovers, was the adventure.
Of course, in order to be a story, there is always conflicts and setbacks and wrong steps and figuring stuff out. But again, those are not central mysteries.
In a mystery, the entire story revolves around some detective solving a "Known Unknown". Somebody killed this guy, who killed this guy is the unknown. When the hero figures that out, the killer gets their comeuppance and the story is over.
Basically, something unexplained happened. The hero is motivated to find the explanation, and the story remains focused on the hero figuring it out, with little else. That may demand travel and new experiences, but all in service of solving the mystery.
An adventure is about exploration, and learning to navigate a new world, new rules, meeting new people. The exploration is often motivated by a search, but the audience knows the point of the search, and the story is about a journey of new places, new knowledge, new cultures or people. It is often about the personal growth of the hero. A travelogue, even if motivated by a problem to solve, is not a mystery.
Even if our hero is just trying to find a way back home; like Dorothy in the Wizard of Oz. In fact, Dorothy is given the answer immediately, go find the Wizard of Oz! How? Just follow the yellow brick road!
Plenty of unknowns, but no mystery to solve there. And in fact, the original advice Dorothy received eventually worked, just not as expected.