Here are a few on this list that you may or may not have heard of before:

• Ashurbanipal’s Library
  
• Ħaġar Qim
  
• Olmec Colossal Heads
  
• Terra Cotta warriors
  
• Subterranean city in central Turkey
  
• Tomb of Sunken Skulls
  
• Sacsayhuaman
  
• Pompeii

And of course as is expected the comments on this video thread are very spirited with lots of different theories regarding the topics covered.  Do you have any ideas on how come of these artifacts were made?  Feel free to comment.