Once on the continent, it's quiet confortable to get on a train. Make sure to check fares: night or evening-fares are almost half the price of the normal ticket. to keep it really cheap you can get a weekend-ticket for about 35 DM which is valid for up to 5 people (i think). The big disadvantage is that you can only take regional trainsto get to hamburg which means it's gonna take some time...
det a three-day underground-train ticket. for one day, and especially when you are a group, take the family-day-ticket.

