The rock towers are called 'karst'. Karst forms when slightly acidic rainwater slowly dissolves limestone rock over millions and millions of years. Water seeps into cracks, widens them, and over time the rock is sculpted into towers, caves, and dramatic cliffs. The same process creates underground caves, and Vang Vieng has many of those too.
Inside the limestone towers are hidden caves. Some are so large that temples have been built inside them. One famous cave called Tham Jang was used long ago as a shelter for local people during a cold, rainy season. Today its walls are covered in a mossy green glow and its ceilings reach high into the dark.
The valley around Vang Vieng is farmed. Villagers grow rice, corn and vegetables on the flat land between the towers. Water buffaloes wander the paths, and children cycle on bamboo bridges over the river. The scale of the mountains makes everything else look very small.
Karst landscapes like this exist in other parts of Asia too - in China, Vietnam and Thailand. Scientists think these towers looked even more dramatic millions of years ago, before centuries of rain smoothed some of their edges.