Celje Castle (also known as Celje Upper Castle or Old Castle) (Slovene Celjski grad, Celjski zgornji grad or Stari grad) is a castle ruin in Celje, Slovenia, formerly the seat of the Counts of Celje. It stands on three hills to the southeast of Celje, where the river Savinja meanders into the Laško valley. Today, the castle is in the process of being restored. It was once the largest fortification on Slovenian territory.