Under the plate of the Main Market Square in Krakow the museum about life and trade of Cracovians in the middle centuries is located.

Among the many exhibits and artefacts, you may see some installations like model of the 15th century Krakow ...

or "Rurmus i rząpie" which there are special constructions for water supply in the old city.

And it is the small piece of great exhibition. If you don't trust, go and check :D