When people think of Vegas, they think of booze and STD's...
When I think of Vegas, I think of places like Red Rock Canyon.
It is just outside of Vegas, a mere 30 minutes. It offers plenty of great hiking trails, gorgeous sights and views, horseback riding, rock climbing, even a driving scenic loop if you aren't the athletic type.
I always make it a point to come out here and do at least one hike when I'm out in Vegas. I love everything about the desert terrain - the weather is always gorgeous. (Though be smart if it is too hot!)
Whenever I'm in Vegas with first timers, I always take them on a drive through the scenic loop. Every time it blows their minds and they admit to never having imagined something so breathtaking so close to the strip.
See?? Nature can be fun. :)