Delos is a place you don't wan't to miss if you are exploring the Greek islands. The entire island is a UNESCO World Heritage Site. Quoting from the UNESCO web site:

"According to Greek mythology, Apollo was born on this tiny island in the Cyclades archipelago. Apollo's sanctuary attracted pilgrims from all over Greece and Delos was a prosperous trading port. The island bears traces of the succeeding civilizations in the Aegean world, from the 3rd millennium B.C. to the palaeochristian era. The archaeological site is exceptionally extensive and rich and conveys the image of a great cosmopolitan Mediterranean port."

I don't have much detail to go along with the photos because I didn't have a guide. I just spent hours wandering the ruins and taking pictures.