Around the expansive world in Guild Wars 2 they've filled all the little nooks and crannies with these little interesting environments. The issue many MMO developers have is a severe lack of detail to particular environments, due to the fact that very few people will actually see all of it. So in guild wars 2 they've introduced Vistas and Jumping puzzles.
Often bundled together in the same areas, Vistas are these activateable cinematics which show you the area around you. Usually a keynote of a particular place of interest nearby and is shown by a triangle on the map. A jumping puzzle is an expansive platforming system which rewards you for going to the end. So in these hard to reach places where vistas are located, they place these hidden jumping puzzles.
They often using varying mechanics and add NPCs to help you along. A great example of all of this is the Jumping Puzzle in Lion's Arch known as Weyandt's Revenge. A ghost leads you through many sections and provides some commentary to the area.
This is a pretty good video demonstrating it:
Upon completion of this particular Jumping Puzzle, you gain a level specific item as well as access to a Karma vendor.
Weyandt's Revenge - Guild Wars 2 Wiki (GW2W)
There are many of these Jumping Puzzles scattered around the world, you can either go out and find them for yourself or there's a relatively handy list on the wiki.
Jumping Puzzle - Guild Wars 2 Wiki (GW2W)
The reason I say it's relatively handy, is because often they are still pretty awkward to find despite the wiki telling you the general area.
Hope this brought some insight into what Jumping Puzzles are.