Stonehenge, an Iron Age structure:

See the bump at the top of the square one? The flat ones on top have indentations on them that fit the bumps: How did they get the flat ones on top? Hm . . . .

Stonehenge actually consists of several concentric circles. The smaller and shorter stones in the middle form another, smaller circle:

The sun comes in through the gap between the stones at the apex of every month.

Dave at Stonehenge:

Next we visit Machu Picchu, Chichen Itza, the Pyramids at Giza, Angkor Wat, and the Great Wall of China, but first we stop by Bath.

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