The World Gate is likely the "Powerful portal" the fairies mentioned, that the Fairy Queen built the Fairy Rings into, in which the fairies mentioned that the fairy rings are "not as powerful as the portal." That likely means that the portal could reach more worlds than the fairy rings can.
I’m not great at this game, but I do love quests.
Actually the "powerful portal" was not the World Gate, but the Portal of Life.
The Portal of Life was closed by Guthix and the end of the First Age, before he went to sleep. The Fairy Queen later stumbled upon the closed frame of this old and powerful portal, using its dormant energy to form the Fairy Rings.
Crondis, mightiest God of the Kharidian Desert!