I think the coldest continent ion our planet is Antarctica, a variety of penguins and elephant seals can only be found there.

I want to take a outdoorgo hikeing there, but the extremely weather lets me know it's impossible for me.

I think "go hiking" is more common than "taking a hike" at least in my area. the second one can also be used to tell someone to go away lol. and "to take a hike" already implies that you will be outdoors, so it's not required - you can say you want to take a hike outdoors, but you can't really say you want to take an outdoor hike.

"extreme" is modifying a noun, not a verb, so it is just "extremely." (most words ending in -ly are adverbs)

and "weather" is a 3rd person singular subject, so "let" has to have the -s at the end