see + do
I've done this as well - including the bike ride back down. It's one of the top experiences you can have on Maui (no pun intended), and worth reducing your mai tai intake the night before so you can get it up before dawn. You get picked up from your hotel somewhere around 4:00 a.m. so you can be at the crater before sunrise. From there, you can see the entire island (if the clouds cooperate), and it's an otherworldly landscape: dusty, rocky, with strange-looking silver plants. Then you get on a bike and ride - coast, really - all the way back down to sea level, shedding layers as the sun rises and the temperature goes up. You actually pass through several climate zones on your way back down, so you watch the vegetation and terrain change - and finally, you're at the beach, surrounded by palm trees and watching the surfers tackle the waves. Pretty phenomenal experience and a great way to understand the natural history of the Maui. P.S. We used Maui Downhill and I was very impressed with their approach to safety. This didn't seem like a particularly dangerous activity (you're not going very fast) but they used an excess of caution to be sure that nothing goes wrong.