I really loved this place. Common entrance fee with Wupatki so its really good value and it has its own visitor centre which has lots of good explanatory information and helpful staff. You cant climb the crater itself which is protected but there is a self guided walk (worth buying the guide for $1 or so) which takes you across the lava field. It was so quiet and peaceful when I visited and you look around not just at Sunset Crater itself but all the other surrounding volcanic remains and the whole plave is very evocative.
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