The entrance is where the metro station's entrance is. I should have probably read better before, because on the day it took me a while to find it! It is free of charge on the first Sunday of the month, as part of Wien Museum. After the information and ticket desk, there's a steep spiral staircase to go down (and one to go up again). It is well presented and looked after, I especially liked the lighting, even if no wall paintings are remaining. Some objects are on display in vitrines in a narrow corridor section, but it is quite difficult to enjoy if it is busy. At the end of this corridor, there's a video on a loop showing the development of the area through the centuries. There's no space to leave your coat and bag, but the visit should not take long anyway.