Rare official postcard (Officielle Ansichtskarte No. 4) of the Brölthaler-Eisenbahn (Bröl Valley Railway), a narrow-gauge railway in the Sieg region of North Rhine-Westphalia. The image shows Schloss Allner, a 15th-century castle on the north bank of the River Sieg near Hennef, viewed across open fields with farm buildings to the left and the distinctive multi-turreted mansion set against wooded hills. Published by Rud. Stolle, Bad Harzburg (Villa Ilse). Back printed in Gothic type: 'Brölthaler-Eisenbahn / Officielle Ansichtskarte No. 4 / Postkarte'. Print reference: I. 1000. VIII. 00. K. — indicating a printing of 1,000 copies dated August 1900. Undivided back. Unposted. An exceptionally rare official railway company postcard from 1900.