I know only a few of the many locations used for Robin of Sherwood. But when I know a new one I will put it up here.

 

Alnwick castle in Northumberland was used
as Nottingham castle.

Bamburgh castle in Northumberland was used as 
the Baron the Belleme's castle in "The Sorceror ".
 

 

Chepstowe castle was used as Belleme's
castle in "The Enchantment".

Bodiam castle was used as Huntingdon
castle in "Herne's son".                        

Kidwelly castle is the castle of
Owen of Clun in "Herne's son".

St. Michaels Mount was the setting for Ravenscar
 Abbey in "The swords of  Wayland"                         

some other locations:

The Leigh Woods in Bristol: Sherwood Forest.
Wells Cathedral: The stairs of the Cathedral were used as the Notingham castle stairs in "The Sorceror"