Mauna Kea, Kailua-Kona

Absolutely must do if on the big island. Need a true 4x4 with 4L. Took a 4Runner with no issues whatsoever. Once up there, highly recommend taking a 1 mile round trip hike to the true summit. Hike is harder then you think given altitude. Was about 42F with 30mph winds in late November, so wear appropriate clothing.

Main reason we chose the Big Island to visit. Absolutely beautiful drive. Going 0 to almost 14k elevation in a short span hurts a bit (drink plenty of water). Snow was on the top but otherwise nice weather (be sure to check website before driving up). Park rangers were very friendly and helpful. You can't go to the actual summit (a bit of a bummer but understandable due to the cultural significance for Hawaiians).

Mauna Kea is situated at higher elevation, so it's possible to experience several seasons in one day as happened recently on my out and back walk from the visitor center to the Keck observatory via the Honua'ula Trail. Perfectly clear skies and mid'40 F at 07:30 AM starting out, but notably dense accumulating snow falling at the summit and for close to two hours while descending. Wind chill effect can put the hiker in sub-freezing conditions in a hurry. Without appropriate layering of garments and covering of extremeties, the situation can become nothing less than perilous. The Honua'ula Trail is largely dry as bone sand and gravel which means hiking boots aren't required, but whatever footwear used should be sealed to prevent tiny rocks and sand from penetrating socks and shoes/boots. Long sleeves, scarf and head cover are critical because the sun is intense. CamelBak or up to half gallon water recommended for round trip. No water source at the observatory, nor along the trail. Any permanent snow cover at the top is dusty, not ready for consumption. Views along the trail are good, with or without cloud cover. Worth the walk and conditions. Sign in and out at visitor center. Free admission currently.

Didn't actually get to go to Mauna Kea because we didn't have a 4WD car. But the park ranger recommended us to do a nearby trail on a hill instead. The views from that were also great but very windy that my ear was ringing. Recommend coming with proper gear.

If you can train for it, hike the trail from the visitor center to the summit. It was amazing, the views, the solitude. Bring plenty of water and food, and try to hitch a ride down (you don't want to walk the trail or road at night). Bring warm clothes for the summit. A life goal achieved!