The largest district in Himachal Pradesh by area is Lahaul and Spiti. It is located in the north-eastern part of the state and has an area of 13,835 square kilometers. The district is sparsely populated with a population of just over 30,000 people. The main towns in the district are Keylong and Leh. The district is known for its beautiful scenery and its remoteness. It is a popular destination for trekking, mountaineering, and camping.
Kangra is the second largest district in Himachal Pradesh with an area of 6,019 square kilometers. It is located in the central part of the state and is home to the city of Dharamshala, the winter capital of Himachal Pradesh. The district is also home to the Kangra Fort, one of the largest forts in India.
Chamba is the third largest district in Himachal Pradesh with an area of 4,420 square kilometers. It is located in the western part of the state and is home to the town of Chamba, the district headquarters. The district is also home to the Chamba Valley, a popular tourist destination.
Mandi is the fourth largest district in Himachal Pradesh with an area of 4,051 square kilometers. It is located in the central part of the state and is home to the town of Mandi, the district headquarters. The district is also home to the Mandi Temple, a Hindu temple dedicated to the goddess Durga.
The answer to the question is Lahaul and Spiti.