Hunting Bosses can be very profitable or simply a social event. Since the bosses don't appear simply when called there can be a waiting period up to an hour, and sometimes more. The respawn time for each monster is different and depends on when it was last defeated.
Usually guildmates team up to vanquish the bosses across the lands. It is also possible to form smaller teams or even show up along and try to steal the loot as it drops. Beware, many Roshers take the boss challenge serious and nothing is stopping them from trying to PL each other to before the Boss apprears to increase their chance at getting the loot.
Each town has it's own unque Boss and the system message inform Roshers when they appear. However, by the time you see the message if you are not already camping at the Boss location it will already be too late by the time you get there.
The higher the boss the better the loot. Everything from carats, EOV's, to high level Arch weapons!
Slobreath, Volcano, and Snow Queen spawn 2.5 - 3.5 hours after their last defeat
Kapilco spawns 3.5-5.5 hours after its last defeat
Ballista and Hellbeast spawn 7.5-9.0 hours after their last defeat
Located in the NorthEast section of Berneo