The girls love climbing in the apple tree in the backyard. Besides feeling like they're in a totally different world, climbing trees is a great lesson in problem solving. They have to figure out how to use the tree trunk and limbs to move higher in the tree.
That's one of the reasons why I love homeschooling them. If they need a break from what they're working on, I send them outside. Often times, they head right to the tree and climb it.
Clearly, it challenges them in different ways...and brings focus and clarity to what they are working on when they come back inside to resume their lesson.