Looking for suggestions for a Berlin walking tour hopefully with not too many people
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.
Berlin offers many various walking tours around many different topics, e. g. districts, history, street art ...
Be informed that every walking tour can show you only a small part of Berlin caused by the huge size of Berlin. It is not like in smaller towns that you can see all main sights by one walking tour. In Berlin you will see max. 6 of Berlin's top 10, and 2 only from distance.
Gendarmenmarkt is still a construction area.
The city_s website offers a Berlin for Beginners tour.
So, if you want to get an overview of the city before deep diving I recommend a HoHo bus tour.
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