ABC's of Hamburg
The St. Pauli-Landungsbrücken (Landungsbrücken = Piers) happen to be another main tourist attractions in the city, it ranks seven in my top ten things to do in Hamburg list. It is also the largest landing place in the port of Hamburg.
From here you will have great views of the port, and you will be able to see the cruise ships that are passing through Hamburg. You will also be able to find the entrance to the Alter Elbtunnel, can get on one of the different ferries (which are covered with your HVV ticket if you purchased it).
The piers are also a nice place to walk around and find a nice place to sit and eat (or have coffee and a pastry) while people watching. It's a nice place overall, and if it's the afternoon, then look for one of the beach clubs and have a drink!
To reach the piers via public transport take: U3, S1, S2, or S3