Sometimes referred to as the Lower Castle (Spodnij grad), this 4th-century structure houses an important branch of the Celje Regional Museum . In the cellar is the City under the City , a complete 3rd-century Roman road brilliantly displayed with excavated statuary and frescoes and parts of the old city walls. On top of these are traces of the medieval buildings up to parts of air-raid shelters built to withstand the bombs of WWII.
On the 1st floor, exhibits trace the history of Celje from the late Stone Age and through Roman Celeia right up to the period of the Counts of Celje. Taking pride of place on the 2nd floor are 18 of the noble skulls on display in back-lit cases.
In the southern wing of the Princes' Palace is the Gallery of Contemporary Art , with thematic exhibitions of both local and foreign artists.
