One place we had seen in nearly every tourist information office since Oslo was Alta - a collection of rock carvings dated some time in the BC. It costs £10 to get in but arrive after the visitor centre closes and you can wander around for free the helpful girl on the ticket desk told me.
I can't say we were that impressed in all honesty - it's not worth the entrance fee but worth a look if you are passing after 5.
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Overnight Location GPS: (69.98171, 23.45260) - Carpark next to recreation area overlooking the sea - other campers present.