This is the 13692nd most frequent German word.
einmalige
"Unique" or "one-time."
In this sentence, 'einmalige' is used as an adjective describing the 'Aussicht' (view) and suggests that it is exceptional or one of a kind.
Die Aussicht vom Berg ist wirklich einmalige.
The view from the mountain is truly unique.
Here, 'einmalige' modifies 'Gelegenheit' (opportunity), meaning that it is rare and special.
Dieses Ereignis war eine einmalige Gelegenheit.
This event was a unique opportunity.
In this context, 'einmalige' describes 'Geschichte' (story), indicating the story's uniqueness.