Dirt next to cavern (6)
I believe the answer is:
grotto
'cavern' is the definition.
(I've seen this before)
'dirt next to' is the wordplay.
'dirt next' becomes 'grot' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'grot'+'to'='GROTTO'
Can you help me to learn more?
(Other definitions for grotto that I've seen before include "Type of cave, often with religious significance" , "Attractive natural, or artificial, cave" , "It's left on Dec 24 by Santa and his reindeer" , "Santa's cave" , "Ornamental cave" .)