I remember walking up Diamond Head. At the start I couldn’t figure out why people were coming down soaked in sweat on such a beautiful day. Halfway up, I knew.
Diamond Head is nothing compared to Koko Head. The “trail” is an old railway bed and you use the ties as steps all the way up. Much steeper climb than Diamond Head. I only got half way up before nausea stopped me. If I was in HI longer and tried every day, I could make it to the top after a few tries. Koko Head is great exercise by itself if you do it every day.