How close it actually is
Hoover Dam sits close enough to Las Vegas that it's comfortably done as a half-day trip, making it one of the easiest 'proper' excursions to bolt onto a longer Strip stay without giving up a whole day.
What there is to do
Beyond viewing the dam itself from the bridge and visitor overlooks, guided tours go inside the structure and explain its engineering and Depression-era history — worth booking ahead if you want the interior tour specifically.
Combining it with other stops
Hoover Dam pairs naturally with a wider loop that can include nearby Lake Mead, making it easy to extend from a half-day into a fuller day trip if you have the time.