Kölner Dom (Ziel Nr. 1934) (in de). sonntagsausflug.at / normedio online & corporate design. Retrieved on 2012-08-15.No name, no license
Cologne Cathedral (Part Two) (in en). zephyrinus-zephyrinus.blogspot.de (2012-11-09). Retrieved on 2012-11-10.Name ok, no license
Städtereise Köln - "Kölle is en Jeföhl" (in de). buswelt.de / Thomas Behne, Maik Kühne, Martin Schröder GbR. Retrieved on 2013-12-19.web.archive.org
2 Tage Köln (in de). buswelt.de / Thomas Behne, Maik Kühne, Martin Schröder GbR. Retrieved on 2015-09-12.Name and licence in popup windows