Stari Pisker is a former prison in the centre of Celje, occupying a tower and adjoining building that date back to the medieval town walls. It functioned as a prison from the late 18th century until the 1990s, making it one of the longest continuously operating detention facilities in Slovenia. The building has been converted into a cultural venue and occasional exhibition space, and the exterior — a rounded tower attached to a sober stone building — is one of the more distinctive pieces of architecture in the old town.
The site's history is layered: medieval defences, Habsburg administration, Nazi occupation, and Yugoslav-era incarceration all left their mark. When exhibitions are on, you can enter the courtyard and see some of the original cells. Even from the outside it is worth pausing — the tower is visible from several angles in the old town, and the building's long, ambiguous history gives it an air that more obviously restored heritage sites sometimes lack.