Step 1: Define mangrove vegetation.
Mangrove vegetation refers to the coastal ecosystems found in tropical and subtropical regions, characterized by salt-tolerant trees and shrubs that grow in intertidal zones.
Step 2: Review the options.
- Western Ghat and Dehradun Valley are not known for mangrove vegetation. They are more famous for other types of forest ecosystems.
- Kullu is also not a region known for mangroves; it's located in the temperate zone of the Himalayas.
- Sundarban, located along the coast of the Bay of Bengal, is home to the largest mangrove forest in the world.
Step 3: Conclude.
Sundarban is the correct answer, as it is the famous region where mangrove vegetation is abundant.
Final Answer:
\[
\boxed{\text{Sundarban}}
\]