Take the Autobahn exit 44 Karlsruhe-Durlach and follow the signs "Zentrum/Stadtmitte" resp. "Schloss". We recommend parking in garage "N"/"Schlossplatz" (address: Am Schlossplatz, 76133 Karlsruhe), the entrance is in the tunnel.
If using public transport, you exit the tram at "Marktplatz" station.
Then it's only a 10 minutes walk in the direction of the Karlsruhe Palace, the party is taking place in the small park right-hand in front of the Schloss.