For those interested in colonial architecture, this part of central Kolkata makes for very worthwhile exploration on foot. Once called Dalhousie Square, B.B.D. refers to the names of three Indian freedom fighters (Benoy, Badal, and Dinesh) who shot a British police inspector-general in 1930. At the center of the square (bagh) is Lal Dighi Tank, where locals wade and bathe in the dodgy-looking, spring-fed water. Most impressive of the surrounding monuments is the Writers' Building, the office of the West Bengal government, which stretches along B.B.D. Bagh North Road; it was built to house the British bachelors imported to serve the East India Company. Across the road is the early-19th-century St. Andrew's Kirk, recognizable by its tall white steeple. At the other end of B.B.D. Bagh North is the General Post Office, with a monumental rotunda; it's thought to be the site of the notorious Black Hole of Calcutta incident. Southwest of the tank is the St. Martin-in-the-Fields-inspired St. John's Church (tel. 033/2243-6098; Rs 10; daily 9am-6pm) and, within the grounds, the tomb of Calcutta's founding father, Job Charnock. East of B.B.D. Bagh, to the south of Lal Bazaar, you'll find numerous tea merchants, where teas from Darjeeling, the Dooars, and Assam are packed and exported. Nilhat House, located behind the Old Mission Church, is the oldest tea auction house in India -- join the action on Monday and Tuesday mornings.