At Minehead, Charles is in a terrible hole (5)
I believe the answer is:
chasm
'hole' is the definition.
(I have seen 'Deep hole' mean 'chasm' so perhaps 'hole' could also mean 'chasm')
'at minehead' is the wordplay.
'at' becomes 'chas' (I can't explain this - if you can you should believe this answer much more).
'minehead' becomes 'm' (head letter of 'mine').
'chas'+'m'='CHASM'
'charles is in a terrible' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for chasm that I've seen before include "Deep fissure; gulf" , "What's split" , "A deep opening in the earth" , "Pit" , "Wide gap" .)