Synonyms of the word 
UNCLIMBABLE → IMPASSABLE - UNPASSABLE - UNSCALABLE - UNSURMOUNTABLE
unclimbable
- adj. Not able to be climbed.
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.
unpassable
- adj. Not able to be passed.
unscalable
- adj. Not scalable, that cannot be climbed.
- adj. Not scalable, that cannot be changed in scale.
unsurmountable
- adj. insurmountable.
If you are interested in words, visit the following sites :
- wiktionary.org/unclimbable For complete definition of a word
- 1word.ws/unclimbable to play with words, suffixs, prefixs, etc.