As mentioned about the Saddle Road, make sure you have a full tank of gas. Rental cars are fine for the visitor centre but 4WD beyond there if you want to get to the summit. A couple of points to remember: Visitor centre is at 9,200 feet. The air is noticably thinner. If there is someone in your group or yourself with any form of respiratory issues, reconsider the trip. The summit is over 13,000 feet! Normal aspirated engines like your rental will be gasping for air when you get to the centre; at least our Impala sure was. And going down: use low gear; slow and steady.

I thought that Mauna Kea was a little overrated. Yeah, its cool being above cloud level, but its hard to breathe at that altitude and it takes quite awhile to get there.

Beautiful at night for stargazers but personally I wouldn't do it again.

Don't try to drive this yourself. The weather can be volatile- as in snow and ice. Dress as if you're going to a ski resort- layers, warm jacket. The astounding view can be blocked by clouds at times. Still - what an experience!

Definitely a must see! You cannot go to Hawaii without experiencing the sunset and the stars on the Mauna Kea! Going to the visitor center is however sufficiant, the view is amazing and you can go for free with your car. The best activity on the island!