Of course the answer is: unit of Krakow History Museum. It is really worth visiting and just recently it received a Certificate of Quality from Trip Advisor. It has an area of more than 6000 metres square and the works cost around 38 million zloty.
Renovation of the underground square began first at 2009 but the museum was opened on 24 September 2010. It turned one of the biggest Krakow atractions into a construction site for a few years but it was worth it.
The main exhibithion is named “In the footsteps of Krakow’s European identity” and it makes you feel like you went back in time seven hundred years ago. When you follow the stairs down you can feel Krakow´s historic atmosphere recreated. It is mostly thanks to many holograms and sounds that are surrounding you from different angles. Also the exhibition allows you to see six hundred models in three dimensions by touching screens placed all around the place.
One of the biggest atractions next to the multimedia exhibit are the medieval tracts. Visitors are able to explore the medieval exhibits by walking over them on glass ramps hanging all over the area. This part of the museum is so unique because it includes remains of medieval constructions.
You can learn more details in here: http://www.mhk.pl/exhibitions/6 and also remember that on Tuesdays the entrance is for free (but only if you book in advance!)
Enjoy your time in Krakow 🙂