The island of Hawaii is bigger than all the others combined, hence its nickname. Much of the island is covered by a series of volcanoes, with Kilauea erupting continually for about 30 years. Consquently, Hawaii Volcanoes National Park is definitely worth a day-long visit.
Many honeymooners enjoy staying on the Big Island's Kona Coast, with its five-star resorts and calmer waters. Indeed, Kona is a great place to stay, and can accommodate for all your wedding plans.
Consider visiting upland Waimea, with its cooler temperatures and nearby Parker Ranch. The Hilo side of the island is also where you'll discover the spectacular Akaka Falls, and Rainbow Falls . . . and if you go there, don't miss the farmer's market in old downtown Hilo for a real glimpse into local-style shopping or buying bunches of tropical flowers at unbelievable prices.
On the other hand, you may just want to relax at your resort and sign up for special spa treatments in your free time. Remember, this island is BIG in comparison to the others. Getting around takes longer . . . but that's part of the beauty and adventure that makes Hawaii special.