Brownstone or something else?

This unassuming brownstone is hiding a fascinating secret. Built in 1847 as a standard single family home, it was acquired by the Inter-borough Rapid Transit authority in 1906. Why did they want the building? Well that's because in 1903 they started construction on the first subway tunnel linking Brooklyn and Manhattan and that tunnel would run underneath the street the house sits on. They needed a way to vent the subway system which is were the house comes in. They gutted the inside and added a ventilation shaft as well as an emergency exit staircase for the tunnel below.