Adult guide reviewed Amtrak when crossing northern America (4,5)
I believe the answer is:
kama sutra
'adult guide' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'reviewed amtrak when crossing northern america' is the wordplay.
'reviewed' indicates anagramming the letters (letters reviewed or revised).
'when crossing' is an insertion indicator.
'northern' says the letters should be written backwards (in a down clue, letters go up or 'north').
'america' becomes 'usa' (United States of America).
'usa' written backwards gives 'asu'.
'amtrak' is an anagram of 'kamtra'.
'kamtra' placed around 'asu' is 'KAMA SUTRA'.
Can you help me to learn more?
(Other definitions for kama sutra that I've seen before include "Sanskrit treatise on the art of love" , "Hindu exotic text" , "the other illustrations" , "Hindu sex manual" , "Ancient Sanskrit text on sexual love" .)