Hop aboard the laziest form of transportation yet invented by man a tube and float down north-central Nebraska's Niobrara River. You'd be hard-pressed to find a more relaxing way to spend the day. What makes the journey especially memorable is that the Niobrara cuts through Nebraska's famous Sand Hills, the massive stretch of dunes that cover thousands of square miles in the state. The sand is overgrown with grass and other vegetation, and on your trip down the river, you may even spot a bison or beaver or two. The National Park Service even promises you'll float past a few waterfalls. Beats going over them.