Alien; fascinating (6)
I believe the answer is:
exotic
I believe this is a double definition.
'alien' is the first definition.
(I know that alien can be written as exotic)
'fascinating' is the second definition.
(thesaurus)
(Other definitions for exotic that I've seen before include "Having a strange beauty" , "Interestingly different or strange" , "Strikingly different or colourful" , "Weird; strange" , "Unusual, foreign" .)