From the Central Station it’s a 20 minutes walk. You can take the metro nr 3, 5 or 15 for 3 stops to ”Groenplaats” than you have to pass the cathedral to the Grote Markt and there we are. Tram cost 3 euros.
A taxi ride takes 10 minutes and cost about 12 euros.
From Antwerp Airport you can only take a taxi, it will take about 15 minutes (depends of traffic) and will cost about 20 euros.
From Brussels International Airport you can take the train every 30 minutes directly to Antwerp Central Station in 30 minutes and will cost 11.20 euros.