The Almkanal is a 12th-century gravity-fed canal system, partly underground, that brings water from the Königsseeache river into the old town for milling, washing, fire-fighting, and (until the 19th century) sewage. The network is the oldest of its kind in central Europe.
For about three weeks every September, after the canals are drained for inspection, sections of the underground network — tunnelled directly through the Mönchsberg — are opened to the public on guided tours. The rest of the year you can follow the open stretches at street level along Salzach quayside.