The correct answer is option 4, the Western Ghats.

The Western Ghats is a mountain range that runs parallel to the western coast of India. It is known for its rich biodiversity and important ecosystems. In fact, it has been declared a World Heritage Site by UNESCO, which means that it is recognized as a place of outstanding universal value and is protected for future generations.

Option 1, the Spiti valley, is a high-altitude desert valley located in the Himalayas in Himachal Pradesh, India. While it is a beautiful region, it has not been declared a World Heritage Site.

Option 2, the Maikal hills, are a range of hills located in central India. They are known for their forest cover and wildlife, but they have not been declared a World Heritage Site.

Option 3, the Shivalik hills, are a mountain range in northern India and Nepal. They are home to a diverse range of flora and fauna, but they have not received World Heritage Site status.

In conclusion, the correct option is 4, the Western Ghats, which has been declared a World Heritage Site for its exceptional natural value.