Indisposed and unknown at a drowned valley in an old Adriatic region (7)
I believe the answer is:
illyria
'an old adriatic region' is the definition.
'illyria' can be an answer for 'region' (I have seen 'Ancient region' mean 'illyria' so perhaps 'region' could also mean 'illyria'). I'm unsure of the 'an old adriatic' bit.
'indisposed and unknown at a drowned valley' is the wordplay.
'indisposed' becomes 'ill' (similar in meaning).
'and' means one lot of letters go next to another.
'unknown' becomes 'y' (algebra).
'at' says to put letters next to each other.
'a drowned valley' becomes 'ria' (I've seen this before).
'ill'+'y'+'ria'='ILLYRIA'
'in' is the link.
Can you help me to learn more?
(Other definitions for illyria that I've seen before include "Adriatic coastal area, scene of Twelfth Night" , "Roman Adriatic province" , "ancient European state" , "Shakespearean night setting" , "Classical Albania" .)