Walking trails are located all arround the park some even lead to the observatory. It is very dark at night. You typically drive to the observatory because it's to dangerous. The observatory is open late at least till midnight.
You can definitely go on trails when there is light. Not sure if you can see milky way. Please check with the observatory for timings as there no fixed timings. The guy who is responsible for closing gate leaves at certain times in summer and winter...
We spent two nights. We walked some of the trails, but not after dark. The observatory is great and the gentleman who is there is very knowledgable and takes the time to answer questions. We have stayed there twice and enjoyed both times.
We stayed pretty late but not to midnight. Just ask the astronomer when you arrive. It is very very dark there and there are wild hogs, cats, etc, in the area. I would drive.
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