Doing a 100km ride is significant, and having a steep hill or set of climbs at the end is demanding.

I havent had to walk to come home (we have two significant short bet very steep climbs to get back to our place) but I have had to ride very slowly.

Eden... I have walked up Baldwin Street in Dunedin (last year in our South Island holiday) - and is damnedly steep - they have steps running up the side of it because steps are easier to walk than the grade - and anyone who has climbed much will know steps are usually more tiring to walk up...

How cars drive up it defeats me, and I think you would kill yourself if you biked down it (uni students have killed themselves in uni parties when they put each other in wheelie bins - for rubbish - and push each other down for "races")