There are several important legal cases that one should be familiar with for the UPSC Law Optional subject. These cases have had a significant impact on Indian law and have shaped the legal landscape of the country. Here are some key cases that you should consider studying:

1. Kesavananda Bharati v. State of Kerala (1973):
- This landmark case established the basic structure doctrine of the Indian Constitution, which limits the amending power of the Parliament.
- The Supreme Court held that while Parliament has the power to amend the Constitution, it cannot destroy its basic structure or essential features.

2. Maneka Gandhi v. Union of India (1978):
- In this case, the Supreme Court expanded the scope of the right to personal liberty (Article 21) to include the right to travel abroad.
- The court held that the right to life and personal liberty is not restricted to mere animal existence but includes a meaningful existence.

3. Golaknath v. State of Punjab (1967):
- This case dealt with the constitutional validity of the First and Fourth Amendments to the Indian Constitution.
- The Supreme Court held that Parliament cannot amend fundamental rights under Article 368 and that the amending power is subject to the basic structure doctrine.

4. Minerva Mills Ltd. v. Union of India (1980):
- In this case, the Supreme Court struck down certain provisions of the 42nd Amendment Act as unconstitutional.
- The court held that there are certain basic features of the Constitution that cannot be amended, even by Parliament.

5. Vishaka v. State of Rajasthan (1997):
- This case dealt with sexual harassment in the workplace and laid down guidelines to prevent and address such harassment.
- The Supreme Court held that sexual harassment violates the fundamental rights of women under Article 14, 19, and 21.

6. Keshavananda Bharati v. State of Kerala (1973):
- This case is famous for the "Basic Structure Doctrine" which states that the Parliament can amend any part of the Constitution but cannot alter its basic structure or framework.

These are just a few examples of the important legal cases that you should be familiar with for the UPSC Law Optional subject. It is essential to study these cases in detail and understand their implications for Indian law.