A paragon: a person or thing representing such a high point.
Synonym of crisis, the decisive moment in the course of an illness.
A high point: the highest point of any range, the most developed stage of any process, or the culmination of any field or historical period.
Full bloom or reproductive maturity.
A mark, such as a line of seaweed, showing the lowest level reached by a body of water.
The nadir or lowest point of something.