A base in Hamburg is a base for three countries
People move to Hamburg for a job or a course and forget that it is a short hop from a lot of Europe. Copenhagen is under five hours by train. Amsterdam and Berlin are both doable for a weekend without flying.
The trick is booking the long-distance tickets the moment they open, usually about six months out, and building the trip around one fixed anchor rather than trying to see everything. A single well-chosen base per trip beats three hotel changes.
This is available in English only for now. A Spanish version will follow.