I'm flying to a friend's wedding in Aachen at the end of June. I only have 2 free days to explore. I arrive to Dusseldorf on Thursday morning, so I was thinking to spend 1 day in Dusseldorf and then 1 day in Aachen. My questions are:
1. How far is the train station from Dusseldorf International airport from which I could get to Aachen HBF? Can I easily get there from the airport?
2. I read that people advise to buy train tickets in advance. Do they get more expensive closer to the departure date? Is there a chance that the tickets to Aachen will be sold out when I buy them on the day of departure? What's the good place to buy them?
3. Any recommendations on what to see in one day in both of these places? I would like to walk around the city. I was looking for some walking guide maps (free if possible) but didn't really find anything yet.
I would really appreciate any info. Thanks.