On July 24th, 1911, Hiram Bingham III announced to the world his discovery of the ruins of Machu Picchu.
Since then they've become the best-known symbol of the Inca Empire, and been declared a World Heritage Site by UNESCO. Nevertheless, archaeologists are still discovering new aspects to them, and many of their features are still unexplained.
If you've never read about Machu Picchu, Wikipedia has a good introductory article, including several very large and spectacular panoramic photographs. Even over a high-speed internet connection, they take some time to load in full size, but they reward the wait with some breathtaking views of the ruins and the mountains surrounding them.
The ruins are on my 'bucket list'. However, since access is difficult and I'm partly disabled as the result of an injury, I suspect I may have to forgo a visit. Pity. Still, if you ever get the chance to visit the ruins, here are some often-ignored things to see.