The name of Košťálov SCI includes four Třebenice hills in total – Košťál (481 m a.s.l.), Jezerka (487 m a.s.l.), Ovčín (431 m a.s.l.), and Sutomský vrch (505 m a.s.l.). On one of them, Košťál, the ruins of a mysterious medieval castle can be found. The first mention of it comes from 1372, when a contemporary Czech writer and chronicler Beneš Krabice of Veitmile recorded a story about his burgrave. However, who built the castle and to whom it belonged is still unclear.