I think the title says it all: if you ever go to Honolulu/Waikiki/Oaho, you HAVE to go up to Diamond Head.
First take TheBus line 23 and get out at "Diamond Head". Costs (Feb 2013) $2.5, so not really much, one way (But: ask the driver ... there are 2 similar stations!)
Then you have to go up beside the street for about 10-15 minutes, through a tunnel, and then you're in the crater, where you enter the park. There you have to pay a small fee (can't remember how much, but REALLY small ... like 2 dollars?!) and then the real hike up the craterside starts. It takes you about 30 minutes till you are on the top of Diamond Head, overlooking Honolulu/Waikiki if you walk fast. The trail is kinda nice, you really won't need hiking boots or stuff like that.
The view from the top is UN-BE-LIEV-ABLE. There's really not much more I can say about it ... other than: if you're near, you HAVE to do it! :)
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