Hey Aniruddha,
To see places in south Goa are :-
Cabo de Rama - Ruins of Portuguese fort
Colva beach
Galgibaga beach
Mahadev temple
Cotigao wildlife sanctuary
Three kings chapel
Palolem beach
Patnem beach
Rajbagh beach
Butterfly beach
And never miss a boat ride in the waters also ...
Happy Travelling Bro!!!
Hi Aniruddha, south Goa is comparatively less explored. The places you should definitely visit in south Goa are following
Agonda and Varca Beach
Dushsagar waterfall
Cabo de Rama Fort and Colva Beach
Madgao and Vasco de Gama
Also there is a very interesting post about discovering south Goa, i'm attaching that post with this comment, you can check it out and plan your trip.