If your looking for old heritage or say architecture then hampi is the best place. Or you can explore the coastal side of karnataka like Karwar, Gokarna, Murdeshwar, Udupi.
Or you can also go to Hyderabad . It's the beautiful city. In Kerala you can see places like Alappuzha which has backwaters n it's another beautiful thing like u can stay in a boat house .
In Tamil Nadu, Puducherry is another best place which has great places to see n good aesthetics.
Hello amit, I'll be happy to answer your travel queries from my experience ☺️. Some of the best places to travel in southern part o India are munsiyari,Munnar, Kodaikanal,Ooty, Thiruvananthapuram, rameshwaram .and never forget to enjoy your stay at luxury boats of kerela.
Lots of places Beach is Kerala and Pondicherry and Coastal Karnataka and Chennai And Mahabalipuram Hilly regions Tamil Nadu : Ooty and Kodaikanal and Valparai and Annamalai Karnataka ; Coorg and Chikmagalur and Lots of places
Kerala : Munnar and Alleppey and Thekkady and Vagamon and lot's of places to see lots of places to see South Indian