The sight of 8,000 human skulls in a glass shrine stuns visitors into silence.

Outside, where cattle usually graze, human bones sometimes come unearthed after heavy rains.

In Cambodia, nine miles (14.5 kilometers) from Phnom Penh, the "killing fields" of Choeung Ek have become a tourist attraction, horrifying and fascinating. Choeung Ek is one of thousands of other such sites around the country where the Khmer Rouge practiced genocide during the late 1970s.

"There are two things you must see in Cambodia," says Scott Harrison, a traveler from Australia. "Obviously one is Angkor Wat. But the other is the killing fields outside Phnom Penh."

In the chronicle of 20th century horrors, Cambodia ranks high. For much of the last three decades, Cambodia has suffered