The gate is situated in the middle of a corridor in a seldom-traveled section of Cybertron which was long ago converted into a "fused organic" state. The gate is invisible until you make physical contact with it, and unless you knew it was there, it would be all too easy to stumble through it and find yourself stranded in the bowels of Unicron, surrounded by deadly bot-spiders. It is strongly implied that the gate is unidirectional (Cybertron-to-Unicron,), though circumstantial evidence favors Unicron's minions being able to reverse its function to return to Cybertron.