Al right dude,
Kona side of the big island -
Actually, the entire big island is a big fricking rock in the water. Hope you have a nice hotel room with a comfy bed to screw each other in..
Plenty of places to hike around over there. I would recommend against a rental car, unless you want to just suffer the headache for one day and do a lap around the island. CUz the roads are for CHIT over there. Actually some of the roads you have to sign release forms from the rental agency absolving you of coverage if you drive on them.
Its all freakin lava rock over there. You can get out and walk up Mt Kiluea or whatever its name is. Caution: After walking one mile of it, it all looks the same.
Please ensure you stay on all marked trails. We hiked it once and my buddy's hat blew off his head, he chased it over the guard rail, slid down 80 feet and held onto a tree branch while the flight for life rescue chopper came and got him. (Yep, true story, he was the one that made Letterman's 10 dumbest things ever list about 2 years ago)
You can go to the resorts and swim with the dolphins and a handful of decent places to eat.
Dont look at the map of the island and go "HEY, Lets go to the other side of the island and see what Hilo is like!" You are white, you will be stabbed.
Honestly dude, I spent a week on the big island and freakin hated it. One of my buddies spent a week there and rented a harley and drove up and down the Mt. and in all the state parks and had a blast.
Lanai -
Will get back on that one... have to try and find my picture book.
Why the hell did you choose the big island instead of Ohau?