The community will have to work as a team in order to build the monolith. About any times can be put in the chest by the Monolith NPC (which can be found in Britain). Scavenging material in order to build the monolith will give you points depending on the rarity of the resource, item, weapon or armor. Points can be spend to buy Artificer items, building modules or special items.
Once the Monolith is fully built, Exodus is spawned. Exodus is one of the hardest Boss. It will spawn in a random dungeon (Destard, Shame, Eventide or Glacia). The set of Exodus ability will depend on the dungeon it's in. After a certain time, Exodus will port itself to a different dungeon which means you will not always be fighting the same boss. Of course, according to it's difficulty, Exodus will drop a large amount of wanted items.