impassable

adjective

1. not passable; not allowing passage over, through, along, etc.: Heavy snow made the roads impassable.
2. unable to be surmounted: an impassable obstacle to further negotiations.
3. (of currency) unable to be circulated: He tore the bill in half, making it impassable.

adjective

1. (of terrain, roads, etc) not able to be travelled through or over