The Sundarbans is the mangrove forest in Bangladesh that is a World Heritage Site and home to the Bengal tiger.
This enormous tidal forest lies in the delta formed by the Ganges, Brahmaputra, and Meghna rivers, along the Bay of Bengal. Its maze of waterways, mudflats, and salt-tolerant trees changes continually under monsoon rains, river sediment, and the tides. The Bangladesh portion was inscribed on the UNESCO World Heritage List in 1997.
The Sundarbans is famous for its Royal Bengal tigers, a population adapted to an unusually aquatic environment. These tigers can swim between islands and may hunt fish, crabs, monitor lizards, and other prey. The forest also supports estuarine crocodiles, Ganges and Irrawaddy dolphins, river terrapins, and hundreds of bird species.
A common mix-up is treating the Sundarbans as belonging only to Bangladesh. The wider forest crosses the Bangladesh–India border, and India has a separate World Heritage property called Sundarbans National Park. The question specifically points to the Bangladesh property.