Seaside location, sunny and happening (8)
I believe the answer is:
brighton
'seaside location' is the definition.
(I've seen this before)
'sunny and happening' is the wordplay.
'sunny' becomes 'bright' ('bright' can be similar in meaning to 'sunny').
'and' says to put letters next to each other.
'happening' becomes 'on'.
'bright'+'on'='BRIGHTON'
(Other definitions for brighton that I've seen before include "Sussex seaside resort" , "South coast city combined with Hove" , "Sussex city (with Hove)" , "Graham Greene wrote ` `........ Rock' '" , "Where the Prince Regent built his Pavilion" .)