hi Helge,
East Midlands Trains serve Kettering from Saint Pancras station
walk up Station Road to Queensberry road, Turn Right onto Queenberry road...
...cross over Headlands onto Broadway
Continue to London Road, (A6003) and turn RIGHT
you will then come to a roundabout with a garage by it (now disused according to google street view), - on your right hand side
cross over roundabout
You will then pass a pub called the wayfarers inn, keep on going till you come to a second roundabout, go over it onto Barton road
there will then be some railings on your right, this is Wicksteed park, the entrance is a short distance on your RIGHT