I lived in Chennai several years near the Marina beach. We used to go for long walk along the walking trails in the beach that leads to the church. We used to go Sunday mass in the church by walking along the Marina beach. See the best tourist attractions in Chennai, which include Santhome Cathedral Church, Marina beach, Elliots beach etc.
If you don't mind walking a bit, you can visit the Santhome Cathedral church and then walk towards the beach. You can visit the Lighthouse at Marina and it would be very interesting to watch the beach and surrounding areas from the very tall light house.
After the light house, the busy area of the Marina beach starts. The beach road and the beach itself extend about 2 km. At the other end of the beach, you can visit MGR Memorial Park.
By the way, if you don't like the crowd and too many shops, then Elliots beach would be a better place for you, which is just a couple of kilometres from Santhome in the opposite direction.