Červený Hrádek, Natural monument and protected area in Jirkov, Czech Republic.

Červený Hrádek is a 69-hectare natural monument in the Krušné Mountains northwest of Jirkov, declared in 2019 and listed under number 6177. Its bedrock is two-mica and biotite gneiss, not sandstone, lying at 352–460 m in the Bolebořská vrchovina. Most of it falls inside the fenced Červený Hrádek game reserve, with open parts east and near Zámecký rybník.

Borek Castle was founded next to the site at the start of the 15th century; Bohuslav Felix Hasištejnský z Lobkovic had it rebuilt as a Renaissance chateau, and Jan Adam Hrzán z Harasova gave the chateau its surviving Baroque form in 1655–1675. The protected area itself was declared by the Ústí nad Labem regional authority on 1 March 2019 and entered in the central nature protection register as number 6177.

The name Červený Hrádek, "red small castle", comes from the chateau beside the reserve, whose grounds hold the landscape park begun in the 1760s. The reserve lies mostly inside the Červenohrádek game reserve, restocked in 1986 and owned by the state forestry enterprise Lesy České republiky. Visitors may enter the fenced reserve freely.

The game reserve area is freely accessible; the parts outside the fence lie on the eastern side and at the southern end near Zámecký rybník. The terrain rises from 352 to 460 metres, and a single unnamed brook drains the valley into the Podkrušnohorský přivaděč.

The bedrock is two-mica and biotite gneiss of the Krušné hory crystalline complex, not sandstone. The reserve protects loose stands with hollow and semi-solitary trees where the brown stink beetle Osmoderma barnabita and click beetles such as Limoniscus violaceus were found, each only in single specimens.