Travel across (8)
I believe the answer is:
traverse
'travel across' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for traverse that I've seen before include "Ski diagonally across (a slope)" , "Move across" , "Extend or bridge across" , "Travel across or pass over" , "In mountaineering, a steep slope to be crossed from side to side" .)