Haleakala is a very special climb. While others found it boring from so many miles, I cherished it. Each section has it's own unique challenges and views. There are only two short sections of slight downhill during the entire 36 miles. Be sure to put your bike in the hardest gear for the photo op at the elevation sign.
The second day of the Everest Challenge up to White Mountain back in 2011. The section somewhere nearish the top where you have the great view to your left. That was about the only thing that kept me going as I was very much done with climbing.
The Alta Alpina 8 pass double century. You climb the back side of Monitor last for the 8th climb of the day. By that time the sun is starting to set and the views are spectacular. The descent back down to Markleeville is in the dark (if you're slow like me).