I am interested in seeing the Kolner Dom in Cologne and am staying in Frankfurt this weekend. It looks like I could make a day trip out of this by train, and I was wondering if someone might have some advice. Is this possible?

After reading several threads and googling a bit, I believe I can hop on the ICE early Sunday morning and head to Cologne, which should take about an hour and 20 minutes. I would then spend a bit of time there and hop on the train back, though I would like to go a bit more scenic to catch the late afternoon light, probably through Koblenz.

Does this sound like it is doable? I don't mind traveling a long way for a short time especially since this would be my first time on the ICE. It looks like I should certainly reserve a spot on the morning Frankfurt-Koln run, but the Web site offers me a full-fare and a discount. Can I purchase the discounted fare, or do I need to meet some criteria. And on the way back, can I purchase my ticket at the station, or should I reserve that, too.

Thanks for any help you can offer.