We present a visualization of subject headings that typically accompany books as flat textual metadata. The purpose of the visualization is twofold: first to expose the implicit structure in subject headings as an overview of a library collection and second to present a visual web of keywords to invite exploration of books. Taking a tag cloud as a starting point, the visualization extends it to a networked tag cloud that respects the hierarchy that is implicit in subject headings. By allowing an information seeker to successively build a subject filter, while seeing the results at each step, we hope to improve the searcher’s orientation in a comprehensive book collection.