My wife and I visited here in August 2017. As it's in use these days as an office building, it's closed to the general public during the week. However, the company urbanguides.nl run tours at 12pm on Saturdays and Sundays, which can be joined for 16 euros per person. Tours last for an hour and can be conducted in English or Dutch, depending on the make-up of the group.
We really enjoyed the tour and being able to see inside! Access to the site is easy, either by bike or by direct bus from Rotterdam Centraal. Limited parking is also available on site for an extra charge.
