travel.stackexchange already informed me 👇🏽
> The question you're asking appears subjective and is likely to be
> closed

I am still taking a chance.

Thank you for your attention. 🙏

I have searched quite a bit on Google, Bing, unfortunately, it will only take me to the flight booking websites.

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I have found the following so far:

* There are no direct flights from San Francisco, US to Cologne, Germany.
* There are few stopover options (connected flights), but very limited in number and time-consuming. 
* There are trains from Frankfurt International Airport to Cologne.
* I am considering flying from San Francisco to Frankfurt and then take a train to Cologne.
* I am puzzled with the train part I am not sure how and from where to purchase tickets.

Any pointer would be very helpful.

Thank you for reading.

Should you still feel this question is not appropriate for this forum, any pointer would be very helpful. Thank you again for your considerations.