As you might know: today 50 years ago, on August 13th, 1961 East German soldiers and workers began to build the Berlin Wall. For the Western World this came as a complete surprise. Not only had Walter Ulbricht, head of East Germany’s government in those days, only weeks before said “Nobody would intend to build any kind of wall or whatsoever.” Additionally it was almost a miracle how such a huge project could be kept so secret – and how it could actually then also get realized without much technical difficulties.
But as a matter of fact: on the morning of August 13th 1961 Berliners woke up in a divided city. And Berlin stayed divided for over 28 years.

border patrol securing Brandenburg Gate when the Berlin Wall was built on 13 August 1961 – photo by Steffen Rehm (Own work) [Public domain], via Wikimedia Commons
If the weather is fine you may also want to take a walk up the area, where the Berlin Wall used to be. Easiest would probably be to arrive at Nordbahnhof (by S-Bahn or Tram or Bus) and then walk up Bernauer Strasse towards Brunnenstrasse. On the way you’ll find many information poins, images, remains — and nowadays quite a number of other people..:)
If you have enough power left you may continue your walk all the way up to the park called Mauer Park — and if it’s Sunday, you’ll find a vast flea market area packed with all kinds of more or less typical Berlin thingies – and more or less typical Berlin people…:]
see also: The Berlin Wall 1961 – 1989