Rent a toboggan for $8. Place it in a concrete slot that's got refrigerator coils inside it (which means that you can sled all winter long, whether there's snow or not). Then invite two to six friends (depending on their size) to come on board with you. Now hold onto your skullcap. The drop-off is roller-coaster steep; you left your stomach at the top. You conservatively estimate your speed at 40 miles an hour. Then shoot out at the bottom of the hill and glide for about a quarter-mile before coasting to a stop. Belly laugh. Repeat.