Explanation:

- Undavalli Caves: These are rock-cut caves, mostly known for their monolithic architecture and impressive sculptures from the Gupta period. Built out of solid sandstone, not limestone.

- Varaha Cave: This is a rock-cut Hindu cave temple in Mahabalipuram. Again, it’s carved from granite, not limestone.

- Borra Caves: This one’s your answer, and you nailed it. Borra Caves are famous natural limestone caves in Andhra Pradesh, formed by the flow of the Gosthani river. Inside, you see fantastic stalactite and stalagmite formations—classic signs of limestone erosion.

- Bhimbetka Caves: These are actually natural rock shelters with prehistoric paintings. The terrain is mostly sandstone, not limestone.

Here's what matters: Borra Caves stand out as India’s best-known limestone cave system. You got it.