I am rather new to this game, and so I am not in a guild, and have little knowledge of their workings, so if none of this is feasible, please just say so.
(For anyone who has played the flash game Dream World, this is somewhat similar to the gates, mines, etc.)

Guild Gates would be a single gate that you guild could collectively open for some sort of fee (probably minerals or CE). Only one gate can be opened by a single guild at a time, and only members of that guild can enter. It is a bit different than other gates, however, being not so infinite and straight forward:

-Each member may enter the gate and fight off various enemies, but at the end of each level is a boss (not as strong as other bosses).
-Bosses are divided into different tiers, with the number of each being dependent on the number of players at a certain level that are active.
-Each boss that is defeated weakens the gate's total strength.
-When the gate is defeated, IDK what could happen. I was thinking a collective boss, but that wouldn't work. I suppose the guild just gets some rewards.

The advantages could be numerous for exploring such a gate as this instead of a normal gate.

-Because they would be Knight-made and not a 'natural' part of the clockworks, they would have much different items and loot, possibly containing rare materials not findable most other places.
-Monsters could be different, offering a change to the same gameplay.
-Allows guild to work as a whole toward a goal.
-Because it is semi-private, it would be significantly easier to control the outcome of the gate using minerals.

That is pretty much it. I know this is a pretty broad overview, but considering how little I know about this game, I don't feel qualified to go much deeper.

Please post constructive criticism or any suggested modifications below!