The Springs Preserve is built on the artesian springs that made Las Vegas possible — the water the Old Spanish Trail stopped for, and the reason the railroad put a town here. The site runs to 180 acres just west of downtown, and it is the most substantial cultural attraction in the valley that most visitors never hear about.
Inside it: the Origen Museum, with a walk-through flash flood exhibit; Boomtown 1905, a re-created early Las Vegas street; botanical gardens organised by desert habitat; miles of trails through the wash; and the Nevada State Museum, included in admission, covering the state from mammoths to atomic testing.
It is a genuine half day if you take the gardens and trails seriously, and it is emphatically a morning visit in summer.