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My first 2-3 months of getting back into shape, did nothing other than run the stairs in my house, 16 stairs in a straight shot, times 80 or 100 or 120 flights or whatnot and I needed days off in between 'cause I was getting tendinitis and stuff. Had to wear loose clothing, wound up soaking 2 shirts in sweat etc.
Personally, I would be able to handle the cardio of your stairs and ladders, but my calves, knees and ankles would NOT hold up without days off. Could. Not. Do it.
And if there were many steps in those 18 flights, up and back down, I can't imagine wearing the same clothes to work in all day :- )