The Fremont Street Experience is what old Vegas is all about.
You can't come to Vegas and NOT at least stop by.
It is nowhere as long as the strip, you can walk it in less than half an hour.
Old Casinos, street performers, a zip line above your head, stuff to see and do left and right.
It's cheaper than on the strip, they still have penny slots, I come here every time I go to Vegas with someone who hasn't been here before.