Civil (CAA) apron hosted in a Military airfield.
Past the civil apron you are in MIL area.
Best and cheapest option for near, well ... sort of near, Athens long or short term Parking and/or Refueling stop (the least expensive aviation fuel prices in Greece).
Overnight stay only by PPR, day visit no PPR needed.
Always check LGMG published NOTAMs for latest info. before flying in/out.
Hangarage may be available by www.globalaviationsa.com
(far east corner of apron) who are also a good maintenance shop primarily busy with the school's fleet maintenance.