I am looking for a word that describes an object that is difficult to stand, walk or balance on due to it's size. The object itself is firmly in place and does not move or wobble, but is still difficult to balance on, let alone walk across it. The object in question is bridge in a video game where the character can easily fall off because the bridge narrow. The word "narrow" may suffice, but I would like a word that makes you feel like it would be almost impractical to balance on it. In this context, the bridge has to be crossed in order to win a reward.
I would offer precipitous here as it seems to fit the description of the situation over a precipice.
Description number 2 here states "a situation of great peril" but is also generally taken to mean on the edge of something that you might fall from.
I haven't been able to find a word for the bridge itself (except for wobbly, which I see, upon rereading the question, you've ruled out). But you might be able to use words that describe the physical act of crossing it: dizzying and vertigo-inducing. Similarly dangerous acts could be called daring, death-defying, or perilous.