Diamond Head

The crater formed in a single explosive eruption around three hundred thousand years ago when rising magma hit groundwater, producing a tuff cone rather than a lava shield - which is why the walls are ash rock and the crater floor is flat. British sailors in the 1800s found calcite crystals in the rock, took them for diamonds, and the name stuck; the Hawaiian name Leahi refers to the ridgeline's resemblance to a tuna's brow. The trail was built in 1908 as part of coastal defence, and it goes through a tunnel and up steep stairs to a fire control station at the summit. Non-residents must reserve a time slot in advance and pay entry, a system introduced to manage the numbers.

What you actually see

• A tuff cone from one eruption - about three hundred thousand years ago.
• A 1908 military trail - through tunnels and up stairs.
• A fire control station - at the summit, from the defence works.
• A name from mistaken diamonds - calcite crystals in the rock.

When to go

Year round; early morning avoids heat and crowds. Two to three hours.

Honest expectations

Non-residents must book a time slot in advance - there is no walk-up. The trail is steep with many stairs and a tunnel, and there is little shade. Midday heat in the crater is severe. It is busy at almost all hours.

Nearby

Waikiki is west; Hanauma Bay is east along the coast.