Both Mid-World and Keystone Earth contain numerous doorways between worlds, divided into two types: Magical and Mechanical. Magical doorways are formed from the substance of the Prim or from the magical tension between two people - the Beach Doors through which Roland drew Eddie and Susannah are examples. Mechanical doorways, created by North Central Positronics, are dedicated to specific locations and mostly one-way only. The tunnels beneath Fedic and Castle Discordia alone contain 595 operational doorways.