vrhunac

1. peak; height; climax
   Bila je na vrhuncu slave kada se povukla. — She was at the height of her fame when she retired.
   Turistička sezona dostiže vrhunac u avgustu. — The tourist season peaks in August.
2. (of a mountain) summit; mountaintop
   Sa vrhunca planine videli smo celu dolinu. — From the mountaintop we saw the whole valley.
3. (in sex) orgasm; sexual climax
   Oboje su istovremeno doživeli vrhunac. — They both reached climax at the same time.

For a literal mountaintop, "vrh" is more common.