Berlin is actually a larger city than Paris and to get to the interesting places you need to use some kind transportation. As a tourist you can buy a “Welcome card”. This is a card you can buy for 15 Euros and use on all public transportations. It lasts two days, but can also be bought for three days. I think it is worth the money.
The outdoor restaurants are many in Berlin and it is interesting to see city people go past. In Berlin you can see all kind of personalities. There are plain characters, business people and teens in crazy outfits. The food how ever is not worth the money, because it does not taste much.
Berlin is a rather grey city, but at night the city lights makes it magnificent and even the rough attitude of city inhabitants seem to get more friendly and open. For someone like me that like photography the city night lights make all the difference, because the photos become magical.