Košumberk Castle, Gothic castle ruin in Košumberk, Czech Republic.

Košumberk Castle is a largely ruined Gothic castle founded in the second half of the 13th century on Košumberk hill (374 m) above the Novohradka valley. What survives is a square tower stump, parts of the palace walls, a gate and remnants of the fortifications, plus the Renaissance purkrabství (burgrave's house) that now holds the castle museum.

The castle was probably founded after 1310 by Ojíř of Košumberk; the oldest dendrochronologically dated wood was felled after 1255 and the first written mention dates from 1312. In 1372 the lords of Chlum, ancestors of the Slavata family, owned it and rebuilt it in late Gothic style. It burned in 1573 and around 1600 a large Renaissance palace was added; in 1684 it passed to the Jesuits, who established a church and residence. After the order was dissolved in 1773 the castle decayed; in 1922 it was donated to the Society for the Rescue of Košumberk Castle and conserved.

The castle gave its name to the Slavata family, lords of Chlum and Košumberk, its 14th-century owners. In 1868 and 1869 national gatherings honouring Jan Hus were held in the grounds. Alois Jirásek set his novel V cizích službách here, and Jiří Šotola's Tovaryšstvo Ježíšovo also takes place at the castle.

The ruin is reached on foot from Luže by a path through the spa park, about 1.5 km, or by car on the road toward Bílý Kůň, with parking at the castle. Buses run from Chrudim, Vysoké Mýto and Skuteč on weekdays; the nearest train station is in Skuteč, 8 km away. A wooden barrier-free footbridge gives access from the south.

The future general Albrecht von Wallenstein was raised here: after becoming an orphan in 1595, his uncle Jindřich Slavata took him in at Košumberk for about two years before sending him to the Latin school in Goldberg. The site also inspired Alois Jirásek's novel V cizích službách and Jiří Šotola's Tovaryšstvo Ježíšovo.