These adventures take place in some of America’s most remarkable environments, so they’ll boost your physique and come with jaw-dropping views as standard Sign up to Simon Calder’s free travel email for expert advice and money-saving discounts Get Simon Calder’s Travel email Get Simon Calder’s Travel email Email * SIGN UP I would like to be emailed about offers, events and updates from The Independent. Read our Privacy notice Forget the hotel gym. There are far more exciting ways of keeping fit