Cruises
Berlin has more bridges than Venice and a cruise is a great way to see the city. Go for an hour or spend all day chugging around, if it's nice.
For timetables see
Stenundkreis
Starlineschifffahrt
Reedereiwinkler
Reederei-riedel
Reederei-triebler
Spreetours
Spree-havelschiffahrt
Nice
website for an overview