What is sought by holy travellers is good mode of transport (5)
I believe the answer is:
grail
'what is sought by holy travellers' is the definition.
I can't judge whether this defines the answer.
'good mode of transport' is the wordplay.
'good' becomes 'g' (abbreviation).
'mode of transport' becomes 'rail' (I've seen this before).
'g'+'rail'='GRAIL'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for grail that I've seen before include "The holy chalice used by Christ at the Last Supper" , "Famous chalice" , "Cherished goal" , "Round Table Knights sought the Holy ....." , "Holy vessel used at the Last Supper" .)