ShotHotspot has mapped 13 abandoned places in Cestica, Varazdin, ranked by how often they're photographed, viewed and voted for. The most popular are Ruins Castle Kalnik, Ruins Tam Public Bath and Maribor Slovenia Graffiti House. Some are private property or unsafe, so get permission before you visit.
We don't know whether you're allowed to visit any of these places. Many are private property, closed to the public or unsafe: get permission from the owner or the relevant authority, and take safety precautions.