In addition to an optional Side Quest you will also have the option to take a Guild Quest at the start of the game. There are Guild Quests for each of the four main Classes (Fighter, Rogue, Wizard, Cleric).
Guild Quests are public (not hidden) and they are designed to give you extra Experience Points for doing the thing your favored Guild does best. For example a Fighter Guild Quest might be “If you defeat a monster with a Fighter using a Weapon you receive a bonus XP.” All players could have the same Guild Quest or they could all be different, or any combination in-between.
The objective of Guild Quests is to provide structure for players as they learn to play the game, and to let expert players maximize their deck strategies. They are a fun, lightweight addition that adds a little extra spice to the Thunderstone Quest experience.