The Frienstein, also called the Vorderes Raubschloss, is a rock formation, about 130 metres high, in Saxon Switzerland.

Around 1410 a watchtower was erected on the Frienstein as a signal station by the Barony of Wildenstein that was owned by the family of Berka of Dubá.

On the eastern side at the foot of the rock is the Ida Grotto (Idagrotte), a large crevice and bedding cave that is nowadays a popular destination.

Because of its size and the fact that it is easy to get to, the Ida Grotto is a popular goal for Boofers, a Saxon term for hikers who sleep out in the open.

However, in recent years, there have been repeated cases of hikers who have fallen and been seriously injured or killed due to being intoxicated with alcohol.