I have some route suggestions for Cologne and the area around. Cologne-Trier (Eifel route) It is a beautiful scenic route with RE and RB passenger traffic using Diesel units. In Euskirchen, the 'Voreifelbahn' from Bonn to Bad Münstereifel is met. Cologne-Koblenz (left side of Rhine) This is a beautiful route alongside the Rhine (especially from Bonn to Koblenz). In Cologne, it includes Cologne-West, Cologne South, and Hürth-Kalscheuren. The NationalExpress operates from Bonn-Mehlem to Cologne Hbf (continuing via Solingen and Wuppertal). A RE line goes from Cologne Hbf to Koblenz Hbf. InterCity lines often drive there and continue to Mainz and further south. Noteworthy stations alongside the route: Cologne Hbf, Brühl, Bonn Hbf, Remagen, Andernach, Koblenz Hbf. A perfect addition would be the Ahr valley line to Ahrbrück. Then the RB service from Bonn Hbf to Ahrbrück via Remagen could be included as well. In addition to that, the line from Andernach to Kaisersesch could be an extension as well, providing another nice valley and an RB service. Cologne-Koblenz (right side of Rhine) The freight services travel largely on the right side of the Rhine, so it is a freight heavy route. But regional services and some IC services are visible as well (Cologne to Koblenz via Troisdorf, Bonn-Beuel). From Cologne Hbf to Troisdorf the S-Bahn runs parallel. The airport loop could be included for extra S-Bahn fun. In case of blockades alongside the left side route, long distance services are re-routed on the right side of the Rhine. To prevent them from having to enter Cologne Hbf from the wrong side, they usually take the southern railway bridge (normally freight only) and then drive once around Cologne (via Cologne West) to enter from the schedule western side of the Hbf. Trier-Koblenz (Mosel route) The Mosel route is another beautiful route with only regional traffic. The last long distance services to Luxemburg were stopped some years back. The route mostly follows the river and comes through Cochem. Short before Koblenz Hbf, a beautiful viaduct is crossed with an amazing view over the valley. Koblenz-Limburg Beautiful route through a forest and serviced by an RB line. It diverges in Niederlahnstein from the right side route to/from Wiesbaden. Koblenz-Mainz (left side of Rhine) The Rhine route continues and passes the legend-rich Loreley. There are RB services calling at all stations, as well as RE and InterCity services. The route also stops at Bingen. Some rare freight services can be seen as well. Additionally, if the high speed line Cologne-Frankfurt is blocked, all ICE traffic has to be routed via the Rhine valley. This increases travel duration significantly. A run with stopping at all stations takes 1h 25 minutes. An InterCity run without any intermediate stops between Koblenz and Mainz takes 50 minutes. Koblenz-Wiesbaden (right side of Rhine) Freight services run alongside the right side route and an RB service can be found as well.