Celje Castle — known locally as Stari Grad (the Old Castle) — stands on a wooded hill above the city and is the largest and best-preserved medieval fortification in Slovenia. The complex dates from the 12th century but reached its greatest extent under the Counts of Celje in the 14th and 15th centuries. The four towers visible from the city below — the tallest of which still stands to its original height — give an impressive sense of scale.
The interior houses a permanent exhibition on the history of the Counts of Celje, with original medieval artefacts, armour, and explanatory panels. But the main reason to come is for the views: from the castle ramparts you can see across the Savinja Valley in all directions, with the city directly below and the green hills stretching to the horizon. The walk up through the forest takes about 20 minutes from the edge of the old town.
The castle is open year-round, though hours vary by season. In summer, occasional concerts and medieval events are held in the courtyard.