The Den Burn stream flows, mostly overground, until it reaches Aberdeen’s West End.
It then dissappears underground before rising up again, momentarily, at Aberdeen Grammar School, before dissappearing underground again and finally entering Aberdeen’s upper harbour.
Many missing sections, underground, and through culverts have still to be mapped.
This query shows work that has been done so far, and sections that still have to be completed https://overpass-turbo.eu/s/VVU .. and a much better, cleaner, query, with decent MapCSS https://overpass-turbo.eu/s/VXi
Town planners, local knowledge, man hole covers, local news papers, and listening for flowing water can all be used to trace streams where access is difficult of the stream is hidden underground.