I was mostly in Hilo, and only in Kona for one overnight, so you’ll have to ask someone else about that!
The Big Island stands out for being the only one with an active volcano, an open telescope observatory on Hawaii’s highest point, and all sorts of weather (including snow!).
The Big Island is also the cheapest of the islands for housing. That’s due in part to the volcano zones where none of the houses can be insured or permitted (which means no bank will give you financing for it), but elsewhere there are houses and apartments outside the danger zone and cheaper.
It’s lesser-known and wetter than Kona (actually it has the most rainfall of any city in the United States) but it works as a tourist town with walkable shop areas, a mall, some restaurants.
I read a million posts telling me to visit Waipio Valley, but was unable to find a place to park. On the west side of the same reserve is this Pololu Valley, which was an immediate win.
Lava Boat Tour
Expensive, sort of controversial now, but the only way to see lava up close with your own eyes. You need to be quick with your camera because steam is pouring out of the sea.
South Point Cliff Dive / Windmills
Beautiful open space, I was saving power on my camera so y’all are missing it.
Black Beach / Green Beach
Not as exciting, but definitely bizarre travels along the south part of the island.
Kalapana House / Chain of Craters Road
At the end of a long Chain of Craters road trail, partially shortened if you rent a fat-tired offroad bike or catch a shuttle van, you can glimpse the lava flowing into the sea. Looks best at sunset and nighttime. You will need a real camera and zoom lens and/or binoculars to get a good look at this. They keep people far away and a lot of people were looking at their phone screens with extreme disappointment.
You are forbidden from getting any closer by this panel of signs and ropes.
The lava fields have a handful of shacks, tiny houses, and other experiments at living off the grid. If you get a chance to stay at an Airbnb or other place in Kalapana, go for it!!
Worth the drive north from Hilo, and the little cash parking fee.
Pu’u O’o Trail
An unexpected adventure for me off of the Saddle Road closer to Hilo than Mauna Kea… I walked many miles over lava, in fields, between different groups of trees. It’s easy to get sunburn or be soaked or lost in the mist here, so come prepared for everything at once. Also good for birdwatching.
Puu Huluhulu (next to Mauna Kea road)
If you are driving the Saddle Road between Hilo and Kona, stop at this volcanic cone next to the Mauna Kea access road. Nice views of the former lava floe and resulting landscape.
Mauna Kea Observatory
Beautiful, surprisingly cold volcanic moonscape. You need your own 4WD vehicle to drive past the visitors center, and any rental car agency will forbid you from doing it. Fortunately you can join tours from Hilo or Kona, either for day or night. The tour groups are strangely determined to make a full day of it, so my Hilo trip made stops at a botanical garden, museum, and the visitors center before heading up the volcano.
Hana Hou Restaurant
This little diner near Volcanoes National Park, the black beach, and the south point of the Big Island, was a really nice place to stop and eat.
Baby Cinnamon Monkey Bread, Maple Bacon Donuts, and other treats in Hilo.
Indian restaurant in the same shopping complex as Lanky’s.
Ken’s Pancake House
24-hour pancakes, also try ahi and eggs, or mahi-mahi specials.
Le Magic Pan
Dessert and savory meals in Hilo:
The lava fields: