Hello, Daniel -
As long as you are taking the time, effort and expense to travel all the way from Germany to Denver, you might as well get your money's worth by adding two or three days to the beginning and/or end of your time in the states to follow Michael Allen's very sound advice (above) and visit the Cumbres & Toltec and Durango & Silverton narrow-gauge railroads while you're here. As Michael noted, the C&TS is about six hours from Denver, and the D&S is only about another 2 hours west of Chama - or 3 to 3½ hours if you stop for a meal in Pagosa Springs on the way,* so it's easily possible to ride the two lines on successive days.
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Rüssell der Zugfanatiker
* If you are like most Germans and enjoy a good beer, I highly recommend stopping for dinner at Pagosa Brewing en route to Durango after riding the C&TS. The brewery has won several state and national awards for its excellent beers, and serves very good food in its pine- and aspen-shaded biergarten.