Yes there are lots to explore. Let me start with temples
Kapaleeshwarar
Parthasarathy temple
Mangadu and Thiruverkadu both are nearby
Mylapore temples like Velleshwarar, karneeshwarar, mundakani Amman temple, kolavizhi amman temple. These temples are around Kapaleeshwarar so when you plan visiting you can cover these temples too. Marundeeshwarar, Madhya Kailash are some temples towards adyar side. While Vadapalani Murugan temple is on Poonamallee side. When you travel to mahabalipuram you can cover Adyar theosophical society,dakshinachitra , Cholamandalam artist village.Dakshinachitra is huge so with senior citizens just plan for two hours inside the premises. Coming to beaches you can plan for Marina sunrise and Besant Nagar beach sunset. It’s Carnatic music season time in chennai so if possible you can view one Kutchery either in Narda gana Sabha or Music academy who have comfortable seatings, but cost of ticket might be high. So if you are planning for Carnatic music program book online prior. Don’t forget to taste best food in woodlands, komalas, Mylapore Karpagam mess, Sangeetha, Arya Bhavan. Shopping at mylapore Mada street is easy when you travel with senior citizens. Other areas are parry’s corner, Ranganathan street t nagar and Pondy bazaar. With rains till December mid better to carry rain wears plus some sweaters for oflate chillness is seen in the city.
Kapaleeshwarar Temple St Thomas Mount National Shrine
Chennai Rail Museum
VGP Marine Kingdom
Guindy Snake Park
Besant Nagar Beach
Pondicherry
Kanchipuram Vedanthangal Bird Sanctuary Safe travels 🙌