The following map shows the important surroundings of the Burg (which is marked red):
As you might have noticed, you have two possibilities to reach the party place: One is to take the Abfahrt Hittfeld when driving along the "Autobahn 1" (); then follow the sign "Veranstaltungszentrum".
The other one is to come on the "Bundesstrasse 4" (). If you come from the north through the "Elbtunnel" via A7 (), you have to leave it at Abfahrt Fleestedt. Then roll down the Hittfelder Landstraße (which is part of the B4) and follow the sign "Veranstaltungszentrum".
Coming by plane, you will use the bus shuttle service to the station Ohlsdorf, wait for the U1, get out at Hamburg Hauptbahnhof and, again, take the S3/S31 to reach Harburg.
If you arrive by ship, then you'll have to take the U3 at Landungsbrücken to reach the Hauptbahnhof.
If you come by spaceship, there is a big area on the other side of the Symposium convention center; please try to land it there (parking is of course free).