Airspace restrictions
Open-category flights are limited to 120 m above the surface unless a national rule permits otherwise. The limit is AGL, not above mean sea level, so flying from a hill does not raise your allowed altitude relative to the ground below. You must stay clear of airport surroundings, control zones (CTR), aerodrome traffic zones (ATZ), and any prohibited, restricted, or danger areas. Temporary restrictions appear in NOTAMs and in U-space or national digital services.
EASA requires geo-awareness: the drone or the operator must be able to identify restricted zones and react to them. Geo-fencing may prevent entry, but it is not a substitute for your own flight planning. National authorities set local distances from aerodromes, prisons, military sites, and sensitive installations, and these distances vary between states.
Traps include: assuming the 120 m limit is AMSL; believing a geo-fence makes a flight automatically legal; forgetting that a NOTAM can close an area at short notice; and assuming that “open category” means “anywhere”. You must also respect no-fly zones over people assemblies and national privacy or security restrictions.
Worked example: your app shows a 120 m ceiling and a nearby CTR. The field is outside the CTR but a NOTAM activates a temporary restricted area over it for a display. You must not fly there during the activation, even below 120 m, because the restriction is separate from the altitude limit.