Uncrossable

There is what appears under normal circumstances to be an uncrossable boundary, a total barrier.

Source: wiktionary

And it’s brilliantly stitched together by motifs of chrysalises and movies and by a joyous abundance of metaphor and simile: “the ding of a bicycle bell like struck crystal”; a woman “talking for much of the day in a steady soft uncrossable stream.”

Source: wiktionary

There are very few bridges on the footpaths in Skye and even short periods of heavy rain can cause rivers to rise rapidly, often making them uncrossable.

Source: wiktionary

There are two Underground stations. That serving the District and Piccadilly is on one side of an uncrossable road called Hammersmith Broadway; that serving the Hammersmith & City is on the other side. Whichever exit you emerge from, at whichever station, you are immediately lost.

Source: wiktionary