The correct answer is option D: Kullu.
The Vashisht hot spring is located in the Kullu district of Himachal Pradesh. It is a popular tourist destination and is known for its healing properties. The water in the spring is said to be rich in minerals and is believed to be effective in treating a variety of ailments. The spring is also said to be a good place to relax and rejuvenate.
The other options are incorrect. Option A: Mandi is a district in Himachal Pradesh. Option B: Chamba is a district in Himachal Pradesh. Option C: Kangra is a district in Himachal Pradesh.
The Vashisht hot spring is located in the town of Vashisht, which is about 10 kilometers from the town of Kullu. The spring is open to the public and is free to visit. There are a number of hotels and guesthouses in the area, as well as a number of restaurants.