In 2011 I've visited Berlin with my school class. It was a five and a half hour bus drive and we stayed in a youth hostel, called "Three little pigs". The hostel was close to the city centre, on the map on the left side you could see that it was only 700 meters away from the Potsdammer Platz.
Because it was a youth hostel it lacked in luxury. We've had to share the rooms and we slept in a bunk bed. The whole building was kinda old and the sanitary could use a renovation. When it got dark outside, the hallways in the building seemed to have something out of a horror movie, it was a bit scary to walk to the toilet in the middle of the night.
But besides the hostel, the city was gorgeous! We've visited all kind of cultural buildings and famous sights. A thing I would really recommend is to hire a bike (€8 a day) or to take part with a cycling tour trough the city (€24). This was you really get to know the inside of the city. You'll come along narrow roads where cars aren't allowed to come and you'll see the most artistic graffiti paintings ever.
Berlin has a rich history, beside the Berlin wall and the holocaust monument, you could also visit a underground bunker from the second world war. Everything is intact and it is really interesting to see how they used to work (and sometimes even live) under the ground.
At least but not last, we've visited a coin museum. They gave us an extensive tour and in the end we've had the opportunity to make our own coin. A nice souvenir to take home.