Drag yourself away from Lego sets and try building something real. Arcosanti is an experimental city in the Arizona desert that is still under construction — perhaps it's time for your shift! Designed to house 5,000 people in an environmentally responsible manner, Arcosanti has been the work of volunteer crews lending their services since 1970. Take a tour of this unique (and walkable) place — you'll learn about alternative energy and urban planning, eat organic food and stay in a room with beautiful desert views.

Recommended for: Urban dreamers of all ages, do it yourselfers and curious kids
Not so hot for: Folks who want a lot of prepackaged activities