Mountaintop, peak, summit.
An antonym for this is a peak or a summit.
base
Lowly, base.
base, headquarters.
Mt. McKinley. The native name for the mountain is Denali.
Ignoble: Base, unworthy.
Base, bottom, or level ground. Those are antonyms of summit.
The antonym base of a mountain refers to the lowest point or bottom of the mountain, often called the mountain's foothill or base camp. It is the opposite of the peak or summit of the mountain, which is the highest point. The base of a mountain typically serves as a starting point for climbers or hikers to begin their ascent.
An antonym for "military base" could be "civilian area" or "peaceful community." While a military base is associated with defense, training, and military operations, a civilian area typically denotes a space meant for non-military, everyday life activities.
base, footing, framework, groundwork, root, support, underpinning
No, departure is when you leave. It is an antonym of arrival.
Driver, if you're talking about riding as a passenger, or base/core if you mean 'rider' as in addendum.