"Greetings, nephalem. Though you have defeated many powerful foes, there remains much to be done. This is a map of Sanctuary and the realms beyond. From here, you can select a region to view it in greater details. This map displays the different places you can go within the region. Locations marked by an exclamation point have bounties for you to undertake. Bounties are the many tasks and challenges which require your attention. In return for completing them, you will be rewarded with powerful items. Good luck, nephalem. Sanctuary has need of you."— Tyrael introduces the mode to the player.(src)
Adventure Mode is unlocked for all characters by completing Act V with any character, regardless of the character level, and once unlocked, can be used by any character of any level of the same type (Hardcore/Softcore and Seasonal/Normal) on account. None of the Campaign Mode storyline quests are available in this mode; instead, special zones can only be found in Adventure Mode:
It is designed to be light on story content, based more around replayability.
There are three map-levels in Adventure Mode: global (a map of Sanctuary), act/region level, and radial (the map of a player's current location). The player has one more layer of automap (world) that allows moving between all five acts at will. All waypoints are unlocked and can be accessed at any time. Horned icons represent bosses and key icons represent Keywardens. Some of the waypoints are misplaced to prevent easy access to bosses.