The Olef Valley Railway (German: Oleftalbahn or Flitsch) or OTB is a 17.8-kilometre-long, single tracked, unelectrified branch line from Kall through the Schleiden Valley above Schleiden to Hellenthal. The line is currently used by tourists; travelling on the heritage railway in the summer months or occasionally by goods trains. However, there are attempts to reactivate passenger services that were ceased in 1981.

• Bernd Franco Hoffmann: Stillgelegte Bahnstrecken im Rheinland. Sutton-Verlag, Erfurt, 2014, ISBN 978-3-95400-396-9.

• Olef Valley Railway
• Schleiden Valley rail and bus initiative
• Rhein-Sieg Railway
• Gutachten Oleftalbahn des Rheinisches Amtes für Denkmalpflege at the Wayback Machine (archived June 26, 2015) (pdf; 121 kB)
• Carsten Klinger (photos), Lothar Brill (text) (2009-08-22). "Bilder der Gemünder Tunnelportale mit Schienenbus, June 2006" (in German). Retrieved 2010-07-28.