From Kassel city centre or Wilhelmshöhe station, take tram line 4 to the Druseltal terminus. On Sundays between 12 noon and 3 pm and on all weekdays until 8 pm, the trams run every 15 minutes. Outside these times, the trams run every half hour.
From Druseltal, buses 22 or 23 will take you directly to the Herkules, where the water features begin. Please note that bus 23 only operates on water play days. Line 23 runs every ten to 30 minutes between 12pm and 6pm. Line 22 runs every half hour between the Druseltal terminus and the Herkules.
On water play days, you can take tram line 1 to the Wilhelmshöhe (Park) terminus. From there, bus 23 will take you to the Herkules via the Druseltal stop.