Wat Phou is a ruined temple complex in Champasak, southern Laos. It is known for its Boun, also known as Wat Phu Festival. It usually takes place on the full moon of the third lunar month (usually in early February for 3 days). Pilgrims from near and far come for Boun Wat Phu, and the festivities include elephant races, water buffalo & cock fighting, boxing, music, and dances. Wat Phou was designated a World Heritage Site in 2001.
I think there is definitely a legend of human sacrifice at Wat Phu Champasak, but there are different versions out there, and the one is known to the locals as “a story about Wat Phou and how the pond or the lake would take one life per year and no more.”
After looking more into this, there is another version; at the top of the temple site are several carved rocks resembling a crocodile, a naga (cobra), and an elephant; it is believed that these rocks were used for human sacrifice.
However, the crocodile stone has acquired some notoriety as possibly the site of an annual human sacrifice. It has been suggested that this crocodile stone was used during the Chenla period (6th to 8th century) to make a human sacrifice (you understand better the deep holes in the rock that would be filled with blood). However, this was never scientifically proved (source.)
I think both legends are interesting; I’m wondering if there is more out there.