The correct answer is option 3: Kathmandu. The SAARC Secretariat, which serves as the coordinating body for the South Asian Association for Regional Cooperation (SAARC), is located in Kathmandu, the capital city of Nepal. The SAARC is an intergovernmental organization consisting of eight South Asian countries, including Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.
Option 1: New Delhi is the capital city of India and is not the location of the SAARC Secretariat.
Option 2: Colombo is the capital city of Sri Lanka and is also not the location of the SAARC Secretariat.
Option 4: Karachi is the largest city in Pakistan, but it is not the location of the SAARC Secretariat.
Therefore, the correct answer is option 3: Kathmandu.