Chhatrapati Sambhaji Maharaj's father, Chhatrapati Shivaji Maharaj, was born in Purandar Fort. However, the user specifically asked about the fort where Sambhaji Maharaj's father was born. Shivaji Maharaj, the father of Sambhaji Maharaj, was actually born in Shivneri Fort, not Purandar Fort. Sambhaji Maharaj himself was born at Purandar Fort. So:

• Sambhaji Maharaj's father, Shivaji Maharaj, was born in Shivneri Fort.
• Sambhaji Maharaj was born in Purandar Fort.

This clarifies the birthplace fort of Sambhaji Maharaj's father.