impassable

adjective
  1. 1

    (of a route, terrain, etc.) Incapable of being passed over, crossed, or negotiated.

  2. 2

    (of an obstacle) Incapable of being overcome or surmounted.

  3. 3

    (of currency) Not usable as legal tender.

Synonyms

Source: https://en.wiktionary.org/wiki/impassable