Wennick Ferry Almanac
The Wennick Ferry Almanac prints the crossing tables, fares, log and lost-property list for the chain ferry across the Wennick narrows. This site is a crawler test: its sitemap is an index that names two child sitemaps, and the second one, /sitemap-b.xml, is broken in every other ten-minute window of the UTC clock.
While it is broken the pages /b1 and /b2 are still online and still correct; only the sitemap that lists them cannot be read. The status page says whether the second sitemap is healthy right now and when that changes.