An interesting variation on a theme there actually! So regarding this concept:

Been to Milan, but never used any airport in the entire north of Italy
Been to Vienna twice but only ever transited once
Been to Toronto but never used any airports in the area either
Been to Tbilisi but never used TBS
Been to Bishkek but never used FRU (although I ALMOST flew FRU-ULN-FRU on a whim, a decision I regret not doing)
Been to Doha but only ever transited through DOH (on unrelated visits)
Been to Kuwait City but never used KWI (the joy of living in Saudi Arabia)
Been around all the Balkan countries (i.e. Serbia, Bosnia, Kosovo, Macedonia, Montenegro, Croatia, and Bulgaria thrown in for good measure) but only ever flew into ZAG once.
Been to Oslo but never used OSL (used TRF instead)
Been to Rome but never FCO (used CIA instead)


Further additions to my own further post:

Flown only into SXF, MDW, TSE, BCN and EVN
Flown only out of GYD, TXL, ALA
Transited only in MUC and PRG (although I exited in PRG due to an 18-hour layover)