First things first. I have seen other reviews that made the drive up to the summit sound like a terrifying and super-steep nightmare ride. I can only imagine that it was snowy and they were unused to driving switchbacks or dirt roads. We had a Ford Explorer and had zero problems or anxiety about the drive up or down. It wasn't particularly steep compared to, say, Rocky Mountain National Park or Costa Rica. We never slipped, always had traction, and the road was never too narrow for two cars to pass. (except in the switchback turns, of which there were few) The 'dirt' road bit is really well packed, and about half of the drive up from the visitor center is paved anyhow.
My wife and I have had altitude issues in the past, but this time we stopped at the visitor center for a half hour (9000ft) and stayed hydrated. We spent a fairly long time at 14k feet with no ill effects. We never got dizzy, nor winded, nor did we get headaches. It *was* cold though! Dress for 40 degree Fahrenheit cooler temperatures than at sea level and wind.
We went to the top of the three parking lots and waited. There were mobile bathrooms up there if you needed them. (If you go on a Saturday or Sunday, you can get a tour of the observatory at the peak instead of just parking there!)
The view was spectacular! Peaks of mountains and the top of Maui sticking up through a sea of clouds! The sunset was spectacular and the cloud level dropped as the air cooled; making the air even clearer! This is really a must-see on the big island! Just beautiful!
Afterwards, we went back to the visitor center for the astronomy and telescopes at nightfall. We saw the stars in a way we never had before! In the middle of Utah, we had seen the Milky Way, but this was the first time we saw the Milky Way, the Accretion Disk, the North Star, and the Southern Cross all in the same place! So many stars! So clear! You could see every meteor and every passing satellite. Cap that off with an astronomer pointing high-powered telescopes at things in the sky and explaining them over hot-chocolate; and you've got an incredible cap to the night's activities! Another must-see!
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.