Fort St. George is a fascinating historical site that dates back to 1644. It was built by the British East India Company and served as the administrative hub of the city of Chennai. Inside the fort, there is a museum where you can learn about the colonial period and see artifacts from that era. There are also some beautiful gardens within the compound that you can visit.
Marina Beach is the second-longest beach in the world and a must-visit for any traveler to Chennai. This beach has a promenade where you can go for a walk while soaking up the sun. There are also various food stalls and street vendors present on the beach to relish some local snacks.
Kapaleeshwarar Temple is a Hindu temple dedicated to Lord Shiva and is an exquisite example of Dravidian architecture. Built-in the 7th century, it is one of the most popular temples in Chennai, thanks to its intricate carvings and beautiful surroundings.
Government Museum is a must-visit place for history buffs. Established in 1851, it houses artifacts from the Chola dynasty, Buddhist artifacts, natural history specimens, and more recent exhibits on the freedom movement.
If you have an extra day, you might consider visiting Arignar Anna Zoological Park, San Thome Basilica, or Guindy National Park.
Ensure you confirm the opening and closing timings of the places before visiting and carry some sunscreen to protect from the sun's harsh rays while exploring the beaches and temples.
If you don't have two full days, you can skip visiting Kapaleeswarar Temple or Government Museum. They are relatively farther apart, so you can also group Fort St. George and Marina beach in the half-day trip and visit one of the above attractions.