This waterfall is in Alna river, called Brynsfossen. As many other falls on the East side, it was used by factories. It passed under the building of Joh. Petersens Lin- og Bomullsvarefabrikk, hence the cache name. More info can be found: here and here.
This is part of AG#25 - Secret Waterfall were clues are placed in the following Waterfall caches:
The cache is a black plastic box, containing a combined micro stashnote/log, pencil and some small trading items.