Cologne help/advice on activities

In about a week, I’ll be going on my first solo trip, also my first international trip! Very excited but equally nervous. Spending about 2 weeks in Cologne. I initially wanted to go because of a three day sporting event there, but figured it’d be the perfect time to make a serious trip like I’ve been wanting to. With no experience, I need some advice on a few things from you all! The event I’m going to requires an EU Digital Covid Certificate to enter, and from the looking I’ve done it sounds like it’s possible for Americans to get that, just have to get a rapid test. Anyone have any experience doing this and advice on how to get it/how long it takes? So, with everything as far as getting there and staying there taken care of, I’m looking for suggestions of things to do the days after the event! I had hoped to do some hiking somewhere for a bit, and I’d like to get to a brewery or something as well. Honestly, just cool places to walk in the city/get something to eat are good to know too! If possible, I’d like to take a day and go to Berlin as well, but not knowing anything about the train systems, I’m not sure how feasible that is. Any advice on getting around Cologne and things nearby to do would be greatly appreciated! Lastly, because of the way the discount on my flights is through a particular airline a family member works for, I’m flying into and out of Frankfurt and plan to take a train to Cologne. From google maps, it looks like there’s a rail station not far from where I’m staying, but the piece I’m missing is how to get from the airport to the station there. Thank you in advance, I can’t wait for this trip to start!

Cologne help/advice on activities