From train station Gent Sint-Pieters, it's a 15-minute walk through Citadelpark.
For certain exhibitions you can buy a B-Excursion ( train + reduced entrance).
For more information check the website of the Belgian railways www.nmbs.be
By Tram or bus
Bus 5, 55-58, 34-36, 70-78
E17 motorway, follow direction Gent Centrum, take exit 1 'alle richtingen', turn left to Citadellaan, and then straight ahead to the Citadelpark