Hahnen Gate
Thirteenth-century city gate whose two round towers still carry a tax-exempt address that broke the numbering sequence.
This guide to the Hahnen Gate in Cologne starts with an address that shouldn't exist: a half-numbered plot from 1795, exempted from Napoleon's building count because officials could not decide who owned a public monument. It traces the gate back to the 1230s, when it was one of twelve openings in an eight-kilometer wall that once watched newly crowned kings ride toward the cathedral, through centuries as a prison, storeroom and slow ruin. By 2006 its crumbling towers had gotten so dangerous that the passage beneath had to be closed. Look up at the carved half-number still visible on the stone today.
Audio guides are written and narrated by AI.