Everyone is going to mention how amazing this is during the day. But just because the sun goes down doesn't mean the enjoyment stops. Watching the Milky Way come out through these magnificent arches and natural beauty is amazing. And not many people live where the Milky Way is visible, so it's an especially amazing treat. If you go at night, make sure you still bring lots of water and some snacks. After all, it is the desert. And take your binoculars. And your imagination. Arches National Park is open 24 hours, so enjoy it. It's a photographer's paradise, day or night.