I would definitely make the trip to Mamallapuram as I would want to see the ancient underwater temples and stone carvings that came into view during the Dec 26 tsunami. Not sure if it's even possible but its something I would want to do.

Also, be forewarned, Mamallapuram, being the coastal town it is, sustained heavy damage from the tsunami and is still recovering.

There is an underground gay scene in Madras - but you'd have to know the locals to get access.

Have a great time!