Your German will need to be up to scratch to read this website, but if not you can get the general idea from having a quick scan & looking at the pictures.

The beer bike is a bicycle made for several people where they are sitting perpendicular to the direction of travel.   The pedalers are the paying public whilst the driver is the tour guide & faces forwards & steering.   A barman serves beer to the pedalers.

It looks like tremendous fun!   Also a great way to tour the city.   They appear to be in most large German cities plus Amsterdam & London (I imagine the London one isn't quite such fun with the traffic & English lager).

Next time I'm in Germanyⁱ I will try one out, but for now have a look at one in action on the following link:

http://www.youtube.com/watch?v=QYROHF4VjTw

I can imagine the best one in the UKⁱ would serve local ale & travel around a smaller , but more spacious town such as Milton Keynesⁱ, Telford or Bournemouth.   Unitl then I can only dream...