Zenith.
peaks...mountain peaks
poo oh there isn't one no, there isn't. oh wait, summit.
Summit
The summit.
zenith
The word you are looking for is "peak" or "summit."
The top of a high mountain is the summit.
I will climb to the summit of the mountain for charity.After several days, the climbers finally reached the summit of the mountain.The emergency summit will discuss the security threats.
Summit
Peak
The summit is the very top of something. Examples include:The hikers reached the mountain's summit after five hours of arduous climbingThe receptionist could barely see the summit of the mountain of papers burying her deskAt the summit of her career, Linda basked in the limelight
The word Zenith means the highest or most powerful point. Nadir means the weakest. Also, Peak, as in a mountain peak.