One of the most ambitious, controversial, and just plain bizarre schemes to hatch in recent years, Biosphere 2 stands in the Arizona desert at the northern foot of snow-capped Mt. Lemmon. Developed in the 1990s by a New Age group called “Synergia Ranch,” and funded by Texas billionaire Ed Bass, Biosphere 2 was originally intended to simulate the earth’s entire ecosystem, in order to test the possibility of building self-sustaining colonies on other planets. A crew of four “biospherians” spent two not entirely self-sustained years sealed inside, but amidst allegations of corruption and deceit, the project has since been redirected to focus on research into the effects of “greenhouse gases” and other ecosystem changes. Media attention and tourist traffic have died down considerably, but you can still visit the very pretty site and take a self-guided tour (daily; $19.95, kids under 5 free; 520/838-6200). To reach Biosphere 2, follow Hwy-79 to Oracle Junction, 25 miles north of Tucson, then turn east onto Hwy-77 for six miles and follow the signs.

  Tucson marks the junction of the US-93 route with our cross-country Southern Pacific route along US-80.