Basic trail switches left to right (5)
I believe the answer is:
stark
'basic' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for stark that I've seen before include "Blunt; grim" , "Severe in appearance" , "Severe looking; naked" , "Unclothed - unvarnished" , "Bleak" .)