What are guild features / guild upgrades?

[Leander]

There are three guild features that can be upgraded up to level 50 each.

1) Fortress:
The higher the level, the more members your guild can have. Each level adds one free member slot to your guild.

2) Treasure
The higher the level, the more gold your guild members receive after quests and work (City guard).

3) Instructor
The higher the level, the more experience your guild members are rewarded after quests (Tavern).