Great place in the summer to get away from the Las Vegas heat.
Tons of great well marked hiking trails to be had, for all fitness levels. Make a stop at the Visitors Center and grab yourself a free trails map or just google it. If you go in the spring time there will be more opportunities to see waterfalls or streams like on the Mary Jane Falls trails and Big Falls.
Take your lunch and eat at one of the many picnic areas or stop by the Mount Charleston Resort and have a bite.
You can even camp up there and make a weekend of it. Plenty of wildlife can be seen at all times of the day.
It's a short drive from Las Vegas so don't hesitate, before you know it, it'll be covered with snow!