BVG is the company who manage the transports in Berlin.
The Berlin WelcomeCard is specially for visitors, is for 48, 72hours or 5 days for AB or ABC zones (AB is enought), includes a guide with up to 50% discount in 130 berliner highlights.
Normal tickets are: sigle Tickets costs 2,10€ and are valid for a maximum of 2 hours, Day Pass (6,10€) or 7-Day Pass (26,20€)
With a Small Group Ticket, up to 5 people can travel together for one day and it costs 15,90€.
All tickets must be validated.
Transports: tickets and rates
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Be careful, Berlin has three zones, A-B-C. The ticket which costs 2,10 is valid just for A-B zones. The A-B-C one, which includes Schönefeld Airport, costs 2,80€.
You must validate your ticket (the Welcome Card too) in the validate machines located at the platforms (red machines) or near the automatic ticket machines (yellow machines).