Replace Bridge Building skill with learnable/teachable class power.
The idea is simple: bridge building is possibly in the top three of the most useless skills in the game.
It serves a single, very narrow goal that can also be achieved with considerably simpler frost bolt spell, either from a spellbook or wand of cold or even with the help of an ogre magi or white dragon.
Instead of having a separate skill for this, I suggest to turn it into a class power that can be learned in the same circumstances as the skill.
When saved, Yrrigs rewards the player with a manual of bridge building, however I do not advocate removing it.
Instead, readying it (an action that causes it to disappear) or agreeing to be taught by the carpenter would result in obtaining a generic
class power instead of a skill.
It could be invoked with ctrl-x and used that way.
Code:
You are able to build wooden bridges.
The probability to construct a bridge section would be fixed, at 75% chance of success.
I believe it's a fair number as the player still has to bring logs around to use as base material and find a hatchet.
It removes the hassle of training the skill for an exceedingly limited potential of use and offers an out-of-the-box one-time usefulness, notably for the tomb of the high kings or early dungeon rivers.
You could even argue that it should be possible to build bridge sections from the right amount of wooden sticks, though they would be subject to similar load bearing issues as ice, to reflect their less than sturdy nature.
Something to improvise with when you are far away from any source of logs.
Trolls could start with the class power as it goes well with lore regarding this race and bridges.
The bridge building skill need not be entirely removed, merely changed into something (potentially) entirely different, useful in a meaningful way.
An example could be Jewelry Making (smithing-like skill that allows to work on improving rings, amulets, bracers etc made of gold and non-metals).
This is of course a very general idea but you get the point. It's useful in a variety of ways and at all stages of the game, something bridge building clearly lacks.