When Guthix created the world, it is believed he also created a gateway through which the many worlds, or universes, could commune. Its only known users are the elves and Humans, who arrived in Gielinor during the First Age. The gate is thought to have been sealed soon after their arrival; whether by Guthix or another is unknown. Since then, none have been able to access Gielinor directly through the world gate. Instead, beings from other worlds have found alternative methods of entering, usually through unstable portals, fairy rings or other means of teleportation.
Whether or not the World Gate will ever be opened again is unknown. If it ever were to be opened, this would open up countless possibilities for Gielinor. The potential dangers of connecting Gielinor to other worlds may have caused the gate to be sealed by Guthix.