I made a ladder. When used it basically makes a slope with a ladder graphic. I made a special action that turns the ladder terrain back into an item that you can carry elsewhere. On the far right of this image you can see that the cliff isn't drawn when there is a slope in front, so I had to add the cliff as part of the ladder graphic. So it looks bad if you don't have the right kind of cliff. Sad day.
Also inside are a couple of debug items that change the elevation of the square you're standing on (like the ladders it these changes won't save when you leave town).
Anyone can use this for anything without giving credit.
There is some chance I'll find a better method (I tried so many different ways already...), if so I'll post it too if I do.
EDIT:
Information about over-under bridge in later post.
Fixed problem with "put_item_on_spot". When you put a ladder where another ladder is, you end up with only one ladder. Fixed by first placing ladder at (-1,-1) then moving it to appropriate square.
Fixed problem preventing one from using ladder where ladder already is (thus loosing ladders)
Code cleanup.
new link: http://speedy.sh/2y4hY/climbtime.zip