The Labyrinth is a subguild of the Mages Guild. It is located through the Library in Moorgate.
Trainers are in the Library at the Spire Of Knowledge where you need to go UP (exit does not show).
Other trainers are found within the four globes which surround the outsides of the labyrinth garden.
Each orb is entered by a command which follows its element (dig, burn, float, and flow)