If "shinny" refers to the act of climbing:
* Opposite: Descend, climb down
If "shinny" refers to a shiny surface:
* Opposite: Dull, matte, rough, cloudy
If "shinny" is a misspelling of "shiny":
* Opposite: Dull, matte, cloudy, rough, opaque
Please provide more context so I can give you a more accurate opposite.