Hi Ellen, we did Essential Berlin (walking) which shows the most important things of the city, It can be done in the afternoon but I recommend you to do it in the morning because in the time that you are traveling darkens earlier ( 3-4 I think). It is not a problem but it is colder. With this tour you can have an good idea about the city. It helped my hotel location so we did not have to take a taxi or bus and our guide met us at the hotel, very close to Postdamer Platz #10. The following day we did The Third Reich. I recommend this if you are interested in WW II's history like is my case. You have to take some subways/trains which is not expensive at all and I suggest to buy a ticket for a day and you can ride all that you want using public transportation. Very interesting. My wife did Potsdam tour ( including Spies' Bridge ) and she had a great experience too. I could not take that tour because I went to a congress so my time was limited. I recommend to contact ViveBerlin Tours and explain what you need. That's what I did and it was a good experience. Our tours were private ( my wife and I ) and the cost for The Third Reich was aprox. 200 euros including tip for a 6-7 hours tour ( all day ). I think the cost is the same if you are 2, 4 or 6. Of course, it is more expensive than big groups but in my personal case it was worth it. Send an email, explain what you looking for, interest, etc; and they are going to offer a lot of options. If I can help you in something more feel free to contact me as you need. I hope it helps. Regards!

Both, it depends on what kind of tour you chose. We did a walking tour ( Essential Berlin ) and also The Third Reich which require transportation ( no included ) by subway or train. We bought a pass for a day and it is inexpensive. It's worth it. I hope it helps and... enjoy it!