I am a not so regular girl settled in US and living the American Dream. My experiences and expressions are my inspiration.
Beaches: The best beaches are along the west coast of the island. However, if you have time, drive south past the volcano national park to black sands beach. It is one of the most unique beaches that I have seen.
Mauna Kea: Be sure to visit the Mauna Kea visitor center and stay past sunset to see the amazing night sky views. You can see thousands of stars and so much more without a telescope. There are organized tours to the summit which can be expensive and they come down to the visitor center for stargazing. If you have a four wheel, you can drive to the summit yourself. You can still drive to the visitor center in a two-wheel from Thrifty since they are the only ones to allow their cars on Saddle Road. Of course, the drive itself can 1.5-2 hours from the west coast resorts to the visitor center. We did the organized tour and were glad we didn't have to drive so much through the desert landscape.
Big Island seems like a very different Hawaii, but there is still so much to do besides the water and beach activities.