Point Sublime is an outcropping that juts out from the North Rim into the Grand Canyon. As such, it's only accessible from May 15th to December 1st.  Although nearly all of the Grand Canyon has Bortle 1 skies, the tourist areas in the park DO emit light pollution that can put a damper on the night skies.
To get to Point Sublime: (and I can't tell you how strongly I suggest you put it on your bucket list!  If you have only one day at the Park AND A 4 Wheel Drive (!!)... honestly.. forget the Visitor Centers and the "must see" spots and go here instead!)... 
It is at the end of an 18-mile off-road 4WD trail.  Yes, you can drive right to it, but you MUST have a high-clearance vehicle and the 'recommended' 4-Wheel Drive.  They are not kidding on this!! I grew up in the mountains of Colorado and I've done a bunch of off-roading.  This trail REQUIRES high clearance and suggested 4WD.  I did it with my 2WD Jeep Patriot - but NEVER again! 

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There are actually 2 trails leading to Point Sublime.  The shortest/fastest route is "Widforss Trail" - the "The 4WD way" as locals call it.  It's 18 miles through forest and you WON'T be driving over 10-20mph, I guarantee it.  The first 7 miles are pretty chill, as are the last 7.  A Subaru Outback could handle those parts..... BUT!!!  The 4 miles BETWEEN those stretches are absolutely 4WD territory!!  There's one particular climb with an extreme grade and scree rock.  It took me 4 times of back-and-forth getting stuck halfway up then spinning out then reversing down the hill to try again.... to get up it, and I eventually had to get a head-start at a very uncomfortable speed to get enough momentum WHILE avoiding some serious "I want to rip out your oil pan" rocks!!  Without the years I spent in the Rocky Mountains, I never would have attempted it - much less made it.
The alternate route (which is how I got back) is considerably longer.  In my opinion, it's rougher.. for a much longer period, but isn't as extreme (if that makes sense).  I didn't have any worries in my 2WD Patriot on the way out.  There are very VERY tight switchbacks making blind turns all along the way, and the road is washboard but only occasional "I better be careful here" moments.  
Here are two good pages that go into more depth regarding directions:

 

Arizona Off Road Net (keep in mind this is written FOR 4WD regulars!)
and
http://www.zionnational-park.com/grand-canyon-sublime.htm