The house of the famous Bengali Jain banking family Jagat Seth. Jagat Seth is a title conferred to Mahtab Rai by the Mughal Badshah(emperor). It literally means the banker or merchant of the world. (Jagat = world, Seth = rich merchant or banker)
There is a secret tunnel in his house which was used for illegal trades. It is currently a museum.
Jagat Seth Mahtab Rai was one of the people that helped Bengal get rid of the unwanted Nawab Siraj-Ud-Daulah by financing the British army of Robert Clive.