*** Østensjøbekken is my 1. contribution to the PPJ-theme: Waterways of Oslo - creeks and rivers. It is the only river which runs out from Østensjøvannet (northside) and into the river Alna at Bryn station together with several others. Well, it it so small, slow and silent, so I guess it should be called a creek.
Most of the creek is closed, but the open water dam where this multicache starts, shows that the river's water power has been used before. From around 1850 it was a chalk factory and a colormill here, and from 1892 Eduard Fett's started Høyenhall factory. It was taken over by his son Harry Fett, who became Norway's first 'National Heritage Councilor' (riksantikvar) in 1912 until 1945. The factory is now closed down, but their beautiful villa Chistinedahl is kept as a memory from these times.
Links to more info on and around Østensjøbekken (in Norwegian): Østensjøbekken, På besøk hos Harry Fett på Christinedal i 1958, m.fl.