Dungeons
Diablo 4 will feature more than 150 dungeon locations covering a variety of tilesets depending on location. Dungeons layouts will be randomised in Diablo 4.
Themes and Tilesets
Dungeons in Diablo 4 will differ from previous games where a single tileset would be present in any one dungeon. Diablo 4 feature what Blizzard calls "tileset transition scenes" which effectively connects two different tilesets together to make dungeons more interesting.
Dungeons can also be be themed depending on where they are in Sanctuary or whether they are tied to a specific cultural theme.
Players can expect dungeons to feel darker and more foreboding with Blizzard embracing Diablo 4's core pillar of a return to darkness.
Multiplayer
Dungeons will be restricted to either their player or their party taking them out of the open world experience.
Dungeon Keys
Players can also use Dungeon Keys to upgrade dungeons to end-game dungeons with different affixes.
Sigils
Sigils are mentioned in the June 2022 developer update as allowing players to upgrade dungeons to make them Nightmare Dungeons where additional affixes are applied to monsters in the dungeon.
However, it's not clear if these have replaced Dungeon Keys or are in addition to.
Known Dungeons
Nightmare Dungeons
The Nightmare Dungeons are considered end-game dungeons.