For 5 days of from 2nd to 6th 18:30-21:00 on May, it is opened in some night of light up of Kanazawa Castle park and the Gyokuseninmaru-garden and Kenroku-en Garden.

Time and place of the Illumination
Time: 18:30 to 21:00 (Entrance until 20:45)
Tuesday, May 2 to Saturday, May 6
Place: Kanazawa Castle Park and Kenrokuen Garden
Admission: Free

Kenroku-en Garden 

Kanazawa Castle park and Gyokusen’inmaru-garden  

Official Ishikawa Travel Guide (Japanese)