The one piece of dry land down which to pass (5)
I believe the answer is:
aisle
'to pass' is the definition.
(thesaurus)
'the one piece' is the wordplay.
'the one' becomes 'a' (a thing is one thing).
'piece' becomes 'isle' (I have seen 'Piece of land' mean 'isle' so perhaps 'piece' could also mean 'isle').
'a'+'isle'='AISLE'
'of dry land down which' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for aisle that I've seen before include "Passage between pews" , "Way between seating areas" , "way to the altar?" , "A key" , "Way between seat blocks" .)