Magical land with a certain invigorating air (5)
I believe the answer is:
ozone
'invigorating air' is the definition.
(I've seen this before)
'magical land with a certain' is the wordplay.
'magical land' becomes 'oz' (I can't explain this - if you can you should believe this answer much more).
'with' says to put letters next to each other.
'a certain' becomes 'one' (ie one particular example of something).
'oz'+'one'='OZONE'
Can you help me to learn more?
(Other definitions for ozone that I've seen before include "bracing atmosphere" , "Gas forming screen against ultraviolet radiation in the stratosphere" , "Atmospheric gas shielding us from ultraviolet radiation" , "invigorating British air" , "Toxic form of oxygen" .)