When someone is unapproachable, you won’t feel comfortable going up to the person and starting a conversation. If a place is unapproachable, it’s really hard to get there.
You’ll notice the word approach is in unapproachable. Approach means “move toward” or “go up to.” When something or someone is unapproachable, that thing or person is hard to get close to. When a place is unapproachable, it’s probably remote or difficult to reach, like a fortress at the top of a cliff. When a person is unapproachable, he or she probably seems unfriendly.