Flendie Clett Castle, Caithness

This castle was located on the island of Stroma.
The 1872 Object Place Name book description is as follows -
A creek, enclosed by an isolated huge portion of rock of the same name has a small portion of foreshore, is used by small boats occasionally.  The summit of Flendie Clett to the same height as the main ???  feature on the coast.  It is said o have been crowned by a castle inhabited by the Vikings or Scandinavian pirates.