The speaker is amazed by one person who seems to understand them completely. This person can tell when the speaker is happy, hurting, or angry just by looking. That is a strange gift for someone who has spent time building strong walls to keep people out. The speaker admits the walls are "unbreakable, or close enough," yet this person passes through them as if they weren't there.
The central image is simple but sharp. Other people, the speaker imagines, stand in front of the wall and ask how to conquer it. This person doesn't fight it. They just walk around. The speaker feels surprise, relief, and some confusion, especially at being able to talk to this person but not to their own family. The mood is quiet and searching, with a hopeful edge. The closing question, "Are we two of a kind?", suggests the speaker senses a shared hurt or experience, and finds comfort in being understood without having to explain.