Go by land that's bleak (6)
I believe the answer is:
wintry
'bleak' is the definition.
(I've seen this before)
'go by land' is the wordplay.
'go' becomes 'try' (I've seen this before).
'by' says to put letters next to each other.
'land' becomes 'win'.
'try' put after 'win' is 'WINTRY'.
'that's' acts as a link.
(Other definitions for wintry that I've seen before include "cool" , "Seasonally cold" , "Cold and icy" , "anything other than friendly?" , "Glacial" .)