Berlin walking tour

You will love Berlin! I had 4 full days and that was not long enough!
I used two walking tours, one for street art and another with a private guide. The latter was very expensive, but very worth it to me. I found the street art tour on the Trip Advisor website. There were about 12 of us, which felt on the larger side.
I also can recommend the Trabi tour- while driving, rather than walking, it was a unique experience and although I feared it would be kitschy the guide was very informative and had a great sense of humor.
My review for the private guide is from early October on the "Day Tour" forum.

The Rick Steves Berlin Audio Europe tour gives a good overview of the major sights:

https://www.ricksteves.com/watch-read-listen/audio/audio-tours/austria-germany

There are other more focused walks in the RS guidebooks covering Berlin.

My personal favorites are Insider Tours, for a group tour and Jeremy the Berlin Expert for private tours.
Have been on 5 of the Insider Tours and gotten so much out of all of them.

We toured with Bernd Gutberlet, and he was fabulous. Highly recommend!

If you are interested in a private tour and have particular interest in the Cold War and the Fall of the Berlin Wall, think about hiring Robert Sommer as your guide. He was the 15 year-old-son of a high-ranking East German bureaucrat when the Berlin Wall fell. Very interesting guy.

His website: http://thetrueberliner.com/

My most recent review of Robert: https://community.ricksteves.com/travel-forum/germany/berlin-guide