If I had to limit myself to the choices above:
Great Wall, China
Pyramids of Giza, Egypt
Taj Mahal, Agra, India
Angkor Wat temple, Cambodia
Stonehenge, Amesbury, United Kingdom
Acropolis, Athens, Greece
Eiffel Tower, Paris
If write-ins were allowed, I would add Mount Rushmore, which to me is more technically difficult than the Statue of Liberty.
I think you just nominated the Interstate Highway System. Which, I admit, should get serious consideration as possibly the single largest government economic development project of all time.
My list:
Angkor Wat temple, Cambodia
Chichen Itza Aztec site, Yucatan, Mexico
Easter Island Statues, Chile
Great Wall, China
Hagia Sophia church, Istanbul, Turkey
Pyramids of Giza, Egypt
Stonehenge, Amesbury, United Kingdom
That was harder than I thought. Dang.
Oh, and let me toss out there that no one who hasn’t seen them in person can properly appreciate the Pyramids. Just seeing them (and climbing them) makes you believe in aliens with advanced construction gear.
One & two:
Three & four:
Five & six:
Seven:
Sorry 
I agree.
I workered there in the 80’s, & it was hard work. But what went on backstage was far more amazing than what went on upfront.