Head out west through town and on about 6km to Santec (passed a small and very odd zoo).
It's a good site (but not municipal) and she will find space for you if you're on a bike, despite not having booked. (She'll mutter a bit). I suppose you could always book if it's in July / August.
The one that was in the grounds of a large house at the top of the hill on the way out of town to the south had closed last time I went passed.