This was Maharishi Mahesh's Ashram, made famous by the stay by the Beatles. It has long since been abandoned and now is being reclaimed by the jungle and graffitiartists. Very cool and spooky!
Entrance fee for foreigners is Rs. 600. Very expensive, and basically a scam by local mafia. Enter for free by climbing a secret staircase from the river, at the left side of a building on the beach.