Follow archaeological tourists, perhaps, becoming glum (4)
I believe the answer is:
dour
'glum' is the definition.
(synonyms)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for dour that I've seen before include "Stern and severe looking" , "Obstinate - grim" , "Sullen, severe" , "Grim and gloomy-looking" , "Gloomy or sullen" .)