Map book includes Northern Territory island — a landmass people have been looking for for a long time (8)
I believe the answer is:
atlantis
'a landmass people have been looking for for a long time' is the definition.
I can't judge whether this definition defines the answer.
'map book includes northern territory island' is the wordplay.
'map book' becomes 'atlas' (I've seen this before).
'includes' means one lot of letters goes inside another.
'northern territory' becomes 'nt'.
'island' becomes 'i'.
'nt'+'i'='nti'
'atlas' going around 'nti' is 'ATLANTIS'.
Can you help me to learn more?
(Other definitions for atlantis that I've seen before include "Legendary vanished island - mythical place" , "Fabled lost city" , "Fabled sunken city" , "In Greek legend, a beautiful island overwhelmed by sea" , "Fabled submerged city" .)