Ognian V.
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This is a surprisingly interesting place, given that I'm not much into sorcery. There's a lot of information in the museum, along with artefacts and items used by "witches". Going through all the information might take you a good couple of hours, but this was an unknown world to me, so I did end up spending more than an hour in there.
There's a nice coffee shop at the ground floor, so if you get tired or just want to clear up your mind from the unworldly experience, this could be a good place do do it.
Parking is free right behind the building.