The sacred Pak Ou Caves of Laos, home to some 6,000 Buddha statues

At least once in their lives, devout Buddhists in Laos strive to visit a very special temple inside a natural landmark, the Pak Ou Caves, directly on the mighty Mekong River, the lifeline of Southeast Asia.

According to estimates, there are as many as 6,000 Buddha statues of various sizes and materials like wood and bronze in two limestone caves, put there by pilgrims over the centuries.

Buddha is depicted with various hand gestures - called mudras - each of which has a specific meaning.

"It is estimated that there are around 4,000 sculptures in the lower cave and around 2,000 in the upper one," says tour guide Somjai Simoonthong, who regularly brings tourists from all over the world here.

The cave temples can only be reached by boat along the Mekong. The journey from the popular tourist destination of Luang Prabang - the former capital of the Southeast Asian country - involves a boat trip of about two hours.

Inside the caves, a Laotian who lives in the US state of Colorado sprinkles a group of Buddha statues with water - as a sign of purification and respect. "I've wanted to travel here for so long, it's very important to me as a Laotian," he says.

Most people in the country believe that their ancestors entered the caves for the first time in the 8th century. At that time, Buddhism was not yet widespread, so the Pak Ou Caves were initially used as a shrine for the river spirits.

After the royal family introduced Buddhism as the national religion in the 16th century, worshippers began making pilgrimages to the caves - especially around the New Year. Many left Buddha statues there, and the cave temple in its present form is the result of centuries of pilgrimages.