Multiple solutions to puzzles (spoliers!)

[gbee]

Immediately after that I noticed that there was a path right beside the gap where you could walk safely.

There was?!? I remember a path down to the lower ledge, but if there was a safe path that didn't require bridge building I completely missed it. I also built a bridge across the gap, boxes on the lower ledge to provide a pillar to support planks laid across. It was pretty fiddly, but I'd already discovered that the barrels could be ignited to keep me warm, so I wasn't in a hurry.

When you exit the library (in Black Plague) you´re supposed to make a see-saw(?) to jump up to a switch that makes a ladder fall down or something. To this day I´ve never solved that puzzle that way.

Hmm, I don't remember that puzzle at all. Was this the library with the secret door?