Huai Pa Tad Unseen in Uthai Thani Province.

Huai Pa Tad is a unique tourist attraction featuring a large limestone cave that visitors must walk through to see the ancient forest hidden inside. This limestone mountain is approximately 245-286 million years old. Over time, rainwater has slowly eroded the rock along its cracks, creating a large cave within the mountain (a process that took hundreds of thousands to millions of years). Eventually, the cave's ceiling collapsed, causing the plants above to fall inside, resulting in the formation of a forest within the cave.