The Summit & Stars Adventure, (808) 331-8505, http://www.hawaii-forest.com, operates year-round, weather permitting. The cost is $192 a person for the seven- to eight-hour trip, which includes dinner.
If you go: Mauna Kea
The Visitor Information Station, http://www.ifa.hawaii.edu/mko/visiting.htm, has exhibits and an informative film. It also offers a free star-gazing program at 6 p.m. daily. Its website has advice on various topics, including altitude sickness, for those wishing to reach the summit.