Take a page from the 20th century: A 10-week guide on how to bring back the adventure of summer.
See the door? Show it to your kids. Remind them there's a whole world out there. A park is probably close by, or a ravine, or maybe a convenience store where they can go buy candy and just sit there on a skateboard getting a sugar high.
No, there's nowhere to plug in a Xbox, which means they're going to have to figure out on their own how to amuse themselves. And yes, it's scary to let them out of your sight. So give them boundaries. Tell them they can only go as far as the park. Follow them if you must, peeking out from behind bushes.
Remember that you spent all day running around as a kid, and it was good for you. You discovered things about the world and yourself that you wouldn't have if you were always shuttled from one structured activity to another. Your kids might, too. Just make sure they're home in time for dinner.