The public transport network in Aachen is often run at a very high frequency throughout the day as well as and a more limited nightly and weekend service.
And here is the one app you will need to get around.
All the data is offline, so worry not about paying through the nose.
And it has all the must see locations in and around Aachen, and how to get there.
With Family Sharing set up, up to six family members can use this app.