Hamburg's excellent tourist information offices can be found in the main station (east exit, Kirchenallee) as well as at the airport (open 06:00-23:00) and in the city centre at St. Pauli Landungsbrücken (between bridges 4 and 5, open 08:00-19:00; Mon, Wed, Sun until 18.00) and at Dammtor station (open 08:00-19:45, Sat 10:00-16:00, Sun closed).
They deal with general enquiries as well as hotel reservations, tickets for events, package tours, hand out maps and useful brochures, and sell the Hamburg Card. You can also call - the phone is manned from 09:00-19:00, Sun closed.