Exit from gate no.2, continue on Rajendra Prasad road and it is located on the right, inside Shastri Bhawan at a short distance
Dr. Rajendra Prasad Road, Central Secretariat, New Delhi, Delhi 110001
Inside Shastri Bhawan
CSL is one of the oldest libraries of the GOI. It is free. you can go and read books but to get subscription you need to be central govt. employee. Timing 9 to 6:30 PM.