Synonyms of the word

unpassable

• adj. Not able to be passed.

impassable

• adj. (of a route, terrain, etc.) Incapable of being passed over, crossed, or negotiated.
• adj. (of an obstacle) Incapable of being overcome or surmounted.
• adj. (of currency) Not useable as legal tender.

unclimbable

• adj. Not able to be climbed.

unnavigable

• adj. (nautical) not navigable; impossible to sail through.
• adj. (of a path, trail, or route) that cannot be used for any reason.

unsurmountable

• adj. insurmountable.

untraversable

• adj. That cannot be traversed.