This little dome is where simulated Mars missions take place. Currently there’s a crew of six living in the dome on a 365-day mission, the longest such experiment to date. The previous crew lived in the dome for eight months.
The dome, at around 8,000 foot on the north side of Mauna Loa, is situated a little way off the Mauna Loa Observatory road. In the photo below it can be seen about ¾ of the way up in the center.
For an interesting article on the Mars simulation mission and its context in history see newyorker.com/magazine/2015/04/20/moving-to-mars. For information about the current, and former, missions, see hi-seas.org.