Inside of gulag has tourists stunned (6)
I believe the answer is:
aghast
'stunned' is the definition.
(I've seen this before)
'inside of gulag has tourists' is the wordplay.
'inside of' indicates the answer is hidden within the clue (I've seen 'inside' mean this).
'AGHAST' is hidden in the letters of 'gulag has tourists'.
(Other definitions for aghast that I've seen before include "'Horrified, shocked (6)'" , "Filled with fear or horror" , "Taken aback with horror" , "Struck with horror" , "Shocked, dumbfounded" .)