It lets you travel by way of south - that's included (4)
I believe the answer is:
visa
'it lets you travel' is the definition.
The definition suggests a singular noun which matches the answer.
'by way of south that's included' is the wordplay.
'by way of' becomes 'via' (via means by way of or by means of).
'south' becomes 's' (abbreviation).
'that's included' means one lot of letters goes inside another.
'via' enclosing 's' is 'VISA'.
Can you help me to learn more?
(Other definitions for visa that I've seen before include "Passport stamp or well-known credit card" , "Addition to passport" , "Travel warrant" , "It allows the bearer to enter the country issuing it" , "Mark on passport" .)