This is the 13869th most frequent German word.
extremste
"Extremste" means "most extreme."
In this sentence, 'extremste' is used as a superlative adjective describing the level of the challenge, indicating it is the most extreme among others.
Die extremste Herausforderung war es, den Gipfel zu besteigen.
The most extreme challenge was to climb the summit.
Here, 'extremste' qualifies 'Wetter' expressing the superlative intensity or severity of the weather compared to other regions.
Diese Region hat das extremste Wetter im ganzen Land.
This region has the most extreme weather in the entire country.
'Extremste' in this case modifies 'Option,' emphasizing the selection of an option that is at the furthest extent of extremity among available options.