Pichavaram is a back water area near Chidambaram. It can be a one day trip if u are visiting pondicherry. Pichavaram is nothing but boat ride into mangrove forest. It's totally a out of india experience as it looks like you are in Amazon forest. The boat guide will take you to the beach area as well as abandoned islands due to sudden rise in sea level where there are millions of red crabs just looking at you. Trust me if u try to go near the island and get down all the crabs will hide inside the mud. No luck catching them. And many Tamil movies like Dasavadharam has been shot here. There is not much to do in pichavaram other than the boat ride into mangroves. There is only one hotel to stay which is highly costly. So I will recommend to stay in Chidambaram or pondicherry instead and take this as a day boat ride visit. I loved this place.