Hennef is a town in the Rhein-Sieg district of North Rhine-Westphalia, Germany. It is situated on the river Sieg, approx. 7km south-east of Siegburg and 15km east of Bonn. Hennef is the fourth-biggest town in the Rhein-Sieg-Kreis . It is the site of the 15th-century castle, Schloss Allner, next to the Allner See.Twin townsHennef is twinned with: Banbury (Oxfordshire, United Kingdom) – since 1981 Heilbad Heiligenstadt (Thuringia, Germany) – since 1992 Le Pecq (Île-de-France, France) – since 1997 Nowy Dwór Gdański (Pomerania Province, Poland) – since 2001