In 1834, Crown Prince Frederick-Wilhelm of Prussia and his brothers acquired the dilapidated ruin. It served as the royal family's hunting lodge and still contains a rich collection of antique furniture, paintings and weapons. The paintings and furnishings of the Koeth-Wanscheid Foundation are displayed on the second floor. This collection includes views of the Rhine, portraits of nobility, and 18th and 19th century furniture owned by a Rhenish noble family. Since 1918, Sooneck Castle has been state-owned and used as a museum. It presents itself as a romantic building, which is embedded in roses like terraces. The rose gardens were laid out on the former bastions of the 17th century. The interiors show how kings used to live away from their court in the 19th century.

Since 2015, every year from summer to fall, a castle blogger takes up residence in Sooneck Castle and in the Ehrenbreitstein Fortress in Koblenz. The blog reports on life in the castle, on the Middle Rhine Valley and its people. The project was developed and realized by the Rhineland-Palatinate Development Agency, the General Directorate of Cultural Heritage and the Rhein-Zeitung.