The decrepit factory is the remains of an old factory that has sunk into the ground and is now mostly radioactive waste. The overall area of the factory is small and there are no internal areas. Take care in the area, as it can reach radiation levels of 72 rads per second the closer one is to the pool of radioactive waste.
Two sensor modules can be found in the small building as well as between 25-50 pre-War money in a duffle bag in a wrecked bus just west-northwest of the factory and south-southwest of the decayed reactor site.
The decrepit factory appears only in Fallout 4.