OUTWARD BOUND
For many, 70 is the new 50, and boomers who have been pushing the envelope — and themselves — since they were kids are not willing to stop just because they're older. For these hardy souls, many adventures await. Some require physical stamina; some require courage; and some just a sense of wonder. Here are 21 thrills throughout North America that range in price from about $25 a day to once-in-a-lifetime splurges.