One of the great things about Berlin is that you always stumble across something related to recent European history when you’re not expecting it. Such was it for me when I discovered the Mauerweg (wall trail): I was looking for a place to hike in and around Berlin that would not entail taking the train for ages to a lake or such in surrounding Brandenburg, and discovered that you can actually hike the course of the former inter-German border, the Berlin Wall, all around former West Berlin.
A well-kept and way marked trail leads you from the urban surroundings of central Berlin to the not-so-urban surroundings of the former border suburbs with fields and biotopes, along landmarks such as the newly built central train station and the Invalidenfriedhof (invalid’s cemetery).
I recommend the central part that runs from Checkpoint Charlie to Mauerpark and is approx. 15 kilometres long, but if you feel like it you can try and tackle all 160 kilometres of the former “Anti-Fascist Protective Barrier”.