Mauna Kea is the site of the worlds 9th largest telescope, occasionally gets snow fall (this is true!), and hands down is the best place to catch both a sunrise and a sunset on the island. Please be mindful of the large altitude difference -- spend some time at the first rest stop to properly acclimate!
We recommend getting there early because parking lots fill up quick and there's no overflow parking! There are some cool trails to hike around. After you've hiked your hearts out, head over to the winery (~10 mins up the road) for unique wine that tastes absolutely amazing (this is coming from your wine-aholic over here)!
While the Florida Keys claim the southern most tip of the U.S. ... they are wrong! South Point on the Big Island is truly the most southern tip of the U.S. at least until the next new island pops out of the ocean! There is amazing cliff fishing and also an area the locals jump into the ocean to cool off (kid you not!!!)
There are many different companies that offer these tours! We did our tour with KONASTYLE whose owner is part of a veteran affiliated nonprofit. KONASTYLE takes off from the pier outside of King Kamehameha hotel and is a nice ride to and from the manta ray location with booze for purchase on the journey! All wedding guests are receiving a 30% discount when doing the tours on September 5 (see our events page for more details).
Just like with the beaches, there are LOADS of coffee farms all over the island and heavily across the Kona side. Some are free while others have an entrance/tour fee. Most have coffee tastings and a few offer roasting sessions! Check out this website to pick the farms you want to tour (Keisha's recommendation - Heavenly Hawaii, Drake's recommendation - Mauka Meadows).
It is quite a hike! About 1.5 hours just to get to the beach - no shade, all dirt paths. There are locals who charge $20/person to drive them in (one way). Please bring proper shoes, sunscreen, lots of water and maybe a little snack!
It's about 2-3 hours to drive to the other side of the island, but it's definitely worth it because the dry side (Kona) and the wet side (Hilo) of the island are two different worlds! If you want to see a little of everything, spend a day driving around the island -- Kona-Waikoloa-Waimea-Honoka'a-Hilo-Keaau-Volcano-Kealakekua-Kona.