Cornish city organised tour crossing river (5)
I believe the answer is:
truro
'cornish city' is the definition.
(I've seen this before)
'organised tour crossing river' is the wordplay.
'organised' is an anagram indicator.
'crossing' indicates putting letters inside.
'river' becomes 'r'.
'tour' is an anagram of 'truo'.
'truo' enclosing 'r' is 'TRURO'.
(Other definitions for truro that I've seen before include "See" , "The Island of Doctor - (H. G. Wells)" , "English city" , "Cornish market town" , "One slain by Cain" .)