Our group went to do the hike on our last day in Honolulu and got there at around 9 am, which is too late. The parking lot is small and it was already full by that time. We were turned away and told to find parking at the base of diamond head. Went down to the lookout point hoping for parking here and again, there was no parking. We ended up leaving and not climbing diamond head at all. It was a big disappointment. For such a popular site, this parking lot should be expanded to allow for more tourists to do the climb. We weren't able to go back as we were leaving the next day.