Šalek Castle, Medieval castle ruin in Velenje, Slovenia.

Šalek Castle is a medieval ruin sitting on a hilltop above Velenje with a distinctive triangular ground plan that sets it apart from typical castle designs. The stone walls and tower remnants are positioned to control views across the Šalek Valley, displaying the structure's former strategic importance.

Šalek Castle is first documented in 1278 as haus Schalekke, already held by the Diocese of Gurk; the Šalek knights, ministerials of Gurk, appear from 1264 with Egeloff de Shelek. In 1314 Nikl of Šalek sold it to Otto Eckenstein, and in 1335 the Bishop of Gurk enfeoffed Frederick of Žovnek. From 1341 the Counts of Celje held it and granted it onward, with the Reichenegg knights residing there until 1428. After 1456 it passed to the Habsburg lands; around 1770 it burned down and was abandoned.

The castle gave its name to the Šaleška dolina, the eight-kilometre valley between Dobrna and Šoštanj, and to the knights von Schallegg, ministerials of the Diocese of Gurk recorded from 1264. The triangular keep appears on Georg Matthäus Vischer's 1681 copper engraving, which still shows a bailey linked to it by a wooden bridge.

A marked trail connects the castle to Velenje at the base, with information boards along the way explaining the structure and its context. Sturdy footwear is recommended since the path climbs a hillside and the ruins require careful footing to explore safely.

The triangular bergfried, the castle's oldest element, has walls up to 2.5 metres thick. Georg Matthäus Vischer's 1681 copper engraving shows a bailey linked to the main tower by a wooden bridge. The ruin is listed as a Slovenian cultural monument of local significance, no. 4329.