The 2585-sq-km Sundarbans Tiger Reserve has 100-plus Royal Bengal tigers lurking in its impenetrable mangrove forests and sometimes swimming its delta channels. Other residents of the forest include Gangetic dolphins, water monitors, 5m-long saltwater crocodiles and luminiscent kingfishers. Entry and guide fees, payable at the reserve's Sajnekhali Ecotourism Centre, depend on which areas you are visiting. If you're on an organised trip from Kolkata, they are normally included in your price.
Overall the best time to visit the reserve is between November and February, though warmer March and April are better for tiger spotting.