Casa Grande Ruins
As is implied by Casa Grande's rather vague assigned name ("Great House"), not even the Spanish had a very clear idea of what it was or why it was built. Modern-day pseudo-scientists speculate that it was an ancient astronomical observatory, but all that's known for sure is that Casa Grande is a big, brown, Indian ruin.
It was a lot of trouble for the Sonoran Desert people to assemble the materials and construct the enigmatic structure, which they did around 1300 AD, just before a severe period of depopulation vacated the region.
Standing in the middle of nowhere, this crumbling, four-story mud skyscraper has always attracted fans of architectural decay. It was the first prehistoric site protected by the U.S. government, back in 1892. What brings Casa Grande into the Roadside realm is the gargantuan steel umbrella that towers over it, built in 1932 by the government to shield it from the sun (Casa Grande would have melted centuries ago if it rained here). The umbrella cost $28,000 to build; now it takes substantially more than that to paint it every year.
Informative tours around this and other satellite ruins are conducted hourly, although no one actually goes into the house, "due to safety and resource protection concerns," according to the National Park Service.
Whatever its original purpose, the ruins of Casa Grand are well-protected for future generations. For them, its most enduring historical mission may turn out to be as a tourist attraction.