📍 Only the Best 10 in Honolulu, HI

Diamond Head State Monument. A volcanic tuff crater formed roughly 300,000 years ago, with a switchback trail up its inner slope leading to WWII-era bunkers and, at the summit, a 360-degree view over Waikiki and the south shore that's genuinely once-in-a-lifetime rather than a replaceable local hike. Five dollars pedestrian entry (parking extra), and an online reservation is now required — this trail got popular enough to need one.

Hanauma Bay Nature Preserve. A collapsed volcanic crater flooded by the sea, protected as a marine life conservation district since 1967 — the calm, reef-sheltered water and sheer density of fish make this one of the best beginner snorkeling spots anywhere on Earth, not just in Hawaii. Twenty-five dollars for non-residents, and both a reservation and a mandatory 9-minute conservation video are required before entry, a direct result of the bay nearly being loved to death before visitor caps were introduced.