This is pretty great, provides a nice set of breadcrumbs for a deep dive into any rabbit hole.
Once thing that threw me off was when I went to the original panel and clicked a second topic, it cleared out the panes that I had explored off the first topic. I had to discover they weren't really lost by re-clicking. I think it would be better if there was some visual indicator they were still there - perhaps the topic (and sub-topics) get collapsed but are still visible with the heading of the selected topic?
Once thing that threw me off was when I went to the original panel and clicked a second topic, it cleared out the panes that I had explored off the first topic. I had to discover they weren't really lost by re-clicking. I think it would be better if there was some visual indicator they were still there - perhaps the topic (and sub-topics) get collapsed but are still visible with the heading of the selected topic?