Each tower of the massive black sandstone Bayon temple at the centre of Angkor Thom is adorned with four giant faces, each of which gazes towards one of the cardinal points with a serene but haunting smile. 37 of the original 54 towers can still be admired. But just who do these smiling faces represent: Jayavarman VII, who built the temple? Or maybe Avalokiteshvara, the bodhisattva of Compassion and a major figure in Mahayana Buddhism? Who knows?