Let’s be real here, everything you do in Guild Wars 2 is some sort of adventure. That’s part of the basic premise of the game; you’re going out and having adventures. But there’s a difference between general adventuring and the upcoming Adventures, which pit players against specific challenges in the game as an evolution of the existing content systems. The designers looked at things like jumping puzzles and skill challenges and saw that while the content was fun, it didn’t have much replay value; hence, Adventures.
Adventures are single-character challenges that emphasize unique gameplay challenges and the upcoming Mastery system; some of them are instanced combat challenges, while others are more about environmental obstacles. They also include leaderboards for you to compare your scores against friends and see if you can do better the next time around, giving players a bit more incentive to go back and try the adventures more than once. Possibly as a sword-wielding Revenant assassin, which was also just unveiled this morning.