I've completed the main mission in Gemcraft Labyrinth and unlocked the first of the 4 corner maps along the way - the other 3 remain stubbornly unavailable. Does anyone know what is required to open them?
The Kongregate forum FAQ thread states that the corner maps are unlocked by earning the following amulets:
A1: L9 Challenge Amulet (Kill 7000 monsters)
A13: Kill 12 Apparitions Amulet
M1: Kill 200,000 monsters Amulet
M13: K9 Challenge Amulet (complete 100 waves)
Note that K9 challenge is not achievable with non-premium, and thus M13 is not unlockable.