Mountain biking across the USA
Mountain biking as a "safer" version of motocross...except for the part where the protective gear is limited, you are miles from medical care, and are often beyond mobile phone service.
The mountain bike is one of the most versatile forms of transportation. It can take you deep into the forests on hiking trails, blitz across wrecked urban terrain, cruise down to the grocery store, and ride pavement for many miles. You can carry it across fences or walls...try that with a motorcycle. You can ride it almost anywhere on national park service trails...excepting a few trails and Wilderness Areas. You can cover in a few hours what would be a day-long "forced march" of hiking.