The Gate is the one and only main entrance to any given Kingdom. It is the first wall that an opposing Kingdom has to break through during war in order to capture the Core. There is one War Chest located there that can only be opened with a War Chest Key which are earned through Warzone events.
For full info on Glorious Slime go to Glorious Slime
The Gate also leads to the Glorious Slime which gives Glory on a daily basis.