Another thing to bear in mind is that if you have a valid public transport ticket, you can actually take a ship run by the local HVV transport network at no extra cost! They leave from the central harbour stops Landungbruecken and Altona Fischmarkt. You can stop off at Neumuehlen/Oevelgoenne to see the beach and go on to Teufelsbrueck, where there's a nice park, the Jenischpark, with its Ernst-Barlach-Museum.