This is the BLOKHUISPOORT in Leeuwarden.
It was a collection of buildings built in 1499 turned into a prison fortress in 1661 till 2008.
Since then, it has been transformed into a cultural hub with retail shops, offices and event/conference space for rent. http://www.blokhuispoort.frl/
There is even a hostel with dorm, shared and private prison cell rooms for your overnight stay. https://alibihostel.nl/en/
A guided tour (Dutch only) is happening every Saturday at 2pm and 4 pm. It costs €10 per person inclusive a cup of coffee/tea and a pastry. http://www.blokhuispoort.frl/gebeurtenis/rondleiding/
Feel free to walk in and have a look around.
Address: Blokhuisplein 40. 8911IJ Leeuwarden.