Taj Mahal's engineering secrets revealed: color-changing marble

The Taj Mahal's 240-foot main dome has acoustics that cause a flute note to echo five times.

Made from white Makrana marble from Rajasthan, the monument shifts colors: soft rose at dawn, white during the day, golden by moonlight.

The monument appears to shrink as visitors walk toward it due to optical illusions.

The four minarets lean outward so that in an earthquake they fall away from the central tomb.

Local legend says Emperor Shah Jahan planned a 'Black Taj Mahal' as his own tomb, though its existence remains unproven.