impassable

adjective3

1. •
   Incapable of being passed over, crossed, or negotiated.

   • At the same time, the encroachment of vegetation proceeds apace, and broom and brambles have already made portions of the line impassable, even on foot. — 1949
2. •
   Incapable of being overcome or surmounted.
3. •
   Not usable as legal tender.