Going through endlessly harsh part of mountain, note it took its toll (6,6)
I believe the answer is:
severn bridge
'it took its toll' is the definition.
(the Severn Bridge was historically a toll bridge)
'going through endlessly harsh part of mountain note' is the wordplay.
'going through' indicates putting letters inside.
'endlessly harsh' becomes 'sever' (I can't justify this - if you can you should believe this answer much more).
'part of mountain' becomes 'ridge' (I've seen this before).
'note' becomes 'nb'.
'sever'+'ridge'='severridge'
'severridge' going around 'nb' is 'SEVERN BRIDGE'.
(Other definitions for severn bridge that I've seen before include "M-four river crossing" , "Route from England to south Wales" .)