Concierge.com's insider take:

Champasak province contains Wat Phou, one of the grandest Khmer ruins outside Cambodia. Though this site doesn't measure up to Angkor Wat, the tumble-down pavilions beneath sacred Phou Kao Mountain are impressive and picturesque. The mile-long temple complex ascends a series of frangipani-lined stone staircases to a sanctuary with panoramic views of the Mekong and the Bolaven Plateau. Wat Phou rests a few miles south of the charming riverside town of Champasak, the former royal seat of a long-vanished Lao kingdom of the same name. Visit during the Wat Phou Festival, on the full moon of the third lunar month (usually early February) to enjoy elephant races and traditional music and dance.