A must see!
I am so fascinated by the engineering that went into building this dam! I wish I had taken the tour inside. You could probably spend a few hours here, it's not really an all day event. You can rent a boat out on Lake Mead and drive up to the top side of the damn. Unfortunately security perimeters won't allow you to look down. But it is still a nice boat ride on the lake.
Even if you are not a geek-tastic person like me, you will still enjoy the awesomeness of this tourist trap. You can take some great pictures and learn a little bit about our history.