Not difficult to go round Mumbai railway station — it’s pure joy (7)
I believe the answer is:
ecstasy
'it's pure joy' is the definition.
(I've seen this in another clue)
'not difficult to go round mumbai' is the wordplay.
'not difficult' becomes 'easy' ('easy' is the opposite to 'difficult').
'to go round' indicates putting letters inside.
'mumbai' becomes 'cst' (I can't justify this - if you can you should give a lot more credence to this answer).
'easy' going around 'cst' is 'ECSTASY'.
'railway station' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ecstasy that I've seen before include "Overwhelming joy" , "Emotional state; drug" , "Feeling of great happiness" , "Feeling of great joy" , "State of euphoria and drug that induces it" .)