Dating back to 1784, St John’s Church (stjohnschurchcni.org; ₹10) retains a large cache of colonial-era history. The two-story, hexagonal Mausoleum of Job Charnock (founder of Calcutta as we know it today) is located in the church grounds, as is the Black Hole Memorial, dedicated to those who died in the Black Hole Prison in the original Fort William.
Within the church, the office of Warren Hastings, the first British Governor General of India, is on the right after you enter. Also look out for the Last Supper painting by 18th-century German artist Johann Zoffany, left of the altar.