What you described is "tough on the knees" going up. You are going up irregular stairs for 4 hours. Some steps are very small vertical rise. Others are 2 feet or more. Some are just toe holds or less. Some move. So there is tension throughout your body in a different sort of way.
Coming down slams the hips - and knees - and legs - and other unheard from before parts of your body. The two directions are very different. Up is lifting and aerobic. Down needs to be a smooth flow instead of individual steps.