Cave reached after crossing river (6)
I believe the answer is:
grotto
'cave' is the definition.
(grotto is a kind of cave)
'reached after crossing river' is the wordplay.
I cannot quite see how this works, but
'river' could be 'r' (abbreviation for river) and 'r' is present in the answer.
'reached' could be 'gotto' ('get to' can be a synonym of 'reach') and 'gotto' is found in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for grotto that I've seen before include "Santa's cave" , "fancy underground area" , "Small picturesque cave" , "It's left on Dec 24 by Santa and his reindeer" , "Ornamental cave" .)