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I think it's further than a half-mile walk to the Strip.
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Yeah, I have no idea what I was thinking. It's closer to a mile. But that's just to the strip itself. You still need to walk on the strip to get anywhere (except Caeasars, which is right there.)
Here's a satellite view of the Rio and its proximity to the Strip:
Map
And yes, it's a busy street and you have to walk on a bridge that goes over the Interstate. It's walkable, but I would never go to Vegas without a rental car. They're cheap and parking is plentiful (and free).