Bicycle touring
Multi-day bike touring is way under appreciated. Touring by bicycle is inexpensive, not difficult, covers a lot of ground and is very satisfying. Great with small groups, too. You can use almost any bike, including ebikes. If you are new to touring on a bike, try following a proven route. For the US go to Adventure Cycling for many detailed annotated routes (where to go, eat and sleep). There is an increasing number of no-vehicle, bikes only routes, which are a fabulous experience. For bike touring in Europe, this overview article Cycling In Europe by Adventure Cycling is the best place to start. — KK