Unlike temporary in-game events, events in CoS are permanent instances you queue for. Of course, victory promises reward. Of the two current events, the Arena is all about survival of the soloist as waves of mobs crash into you whereas Tesla Defense is a five-man tower defense. When patch 1.3 releases, the PvP-based Siege of the Spire will join the event lineup as a MOBA-inspired arena that includes mobs, turrets, and team bases. Players can join the regular events as well as daily and weekly events with larger rewards. For more details, check out the official site.