Talking into a tunnel is when you create something with the intention of honing your craft and not necessarily appealing to an audience. You might let them listen, but you are not concerned with their response. This is what I do with my podcast. I am talking in a tunnel. I am not concerned with what people think of it, I am concerned with developing my philosophy, mindset, content and ideals. When I talk into a tunnel it gets me better at my overall goal. When you podcast is makes you a better orator so when someone asks you a question about a specific topic you know how to articulate what you believe better than had you not done a podcast.
If i make a rap song or rap album, one album might be to provide a contract from my art to that of a fake artist. If I make another, it may have an entirely different motive, such as exercising certain thoughts I have on specific issues. It may not have anything to do with commerical outcome. It's basically me just balancing out my beliefs.