Monument of mystery

Some 5,000 years have passed since the Neolithic people of the Salisbury Plain stood up the slabs that compose Stonehenge, and even after centuries of study, we're still not quite sure why or how. One clue is that upon the summer solstice, its Heel Stone—the squat rock at right—aligns perfectly with the sun and the monument's center point. Many archaeologists believe this was part of its function as a primitive star observatory—but other theories abound, including that it was designed for meditation, burial, or even great acoustics.