If you've got 6' you should be able to build a pretty steep but safe stairway. I just built one that's 8' high and 8' long and it's quiet comfortable to
go up and down. You should be able to use 2x6 treads and actually have a stairway that is fairly normal. It would not be the greatest for going down as the treads will be very short horizontally but a fairly normal vertical step height is possible. Making it easy to go up quickly and doable if you take your time going down... not nearly as much of a ship's ladder as you think.
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