A site often used by the West Hawai'i Astronomy Club is the Pu'u Kuainiho site just off the Mamalahoa highway. The site is located directly beside a small Pu'u, or cinder cone, that occupies the northeastern horizon. A simple gravel lot provides a large area just off the highway with enough space to setup dozens of telescopes while a gravel burm blocks most of the light from passing vehicles. the site offers easy access, wide horizons, and is high enough (2,600ft or 800m) to be above the worst of the tropical haze.
The site is on state DLNR land and is accessed by getting a permit from the local DLNR office in Waimea. A simple cable gate controls access to the site with the key being provided with the permit. Additional gravel was spread on the site by the state to improve the area for observing at the request WHAC. The result is a reasonably good area for telescope use, though the gravel is coarse and you may need to police your area for larger pieces while it is still light to prevent stumbling on a big rock in the dark.
Setting up on the far end of the lot will allow you to be almost 100yds off the highway and out of any headlights, though there is still some ambient light when traffic is passing by. Otherwise the site is very dark as there are no lights of any significance nearby with the resorts along the coast and the streetlights of Waikaloa and Waimea seen as clusters of yellow lights in the far distance.
The site does have some drawbacks, being lower in elevation transparency the sky here can suffer from some low altitude tropical haze impacting transparency, though not nearly as badly as locations along the coast. Dew is often a problem and dew removal gear may be required. Seeing is usually fair to good but seldom any better. The site will often be cloudy in the evening with orthographic clouds formed by the mixing of the cooler high altitude air mass with the coastal tropical humidity forming a cloud deck around 5-8 thousand feet. These clouds will usually break up after dark leaving the sky clear for the remainder of the night. While not as pristine as the higher elevation sites on the side of Mauna Kea, the Pu'u Kuaniho site offers a compromise between better skies and the need to drive an hour up Saddle Road. The weather at this lower site is correspondingly much warmer and less windy if conditions on the mountain are untenable.
If weather threatens down below the backup plan is an hour drive up to the VIS from Pu'u Kuainiho if you really have to have a night out under the stars.
