Group excursions after vacation in river (6)
I believe the answer is:
ganges
'river' is the definition.
(Ganges is an example)
'group excursions after vacation' is the wordplay.
'group' becomes 'gang' (gang is a kind of group).
'after vacation' says to hollow out the word (remove centre letters) (the inside letters must vacate).
'excursions' with its centre removed is 'es'.
'gang'+'es'='GANGES'
'in' is the link.
(Other definitions for ganges that I've seen before include "River flowing into the Bay of Bengal" , "Hindus' most sacred river" , "Indian flower" , "Holy river on India" , "Holy Indian river" .)