The Infamous Acts and their landscape
This area is reminiscent to the landscape found within the first diablo's town, Tristam. As it so happens, Tristam is in the first act and is the location of which you must find and rescue Deckard Cain from his captors. The area appears to be like your typical forest area, quite green but nothing exotic. The architecture features eroded stone buildings and burnt down log houses. Andrial can be found deep within the catacombs, protected by her minions.
: The following area is a plain and relatively dull desert and it features the expected monsters (Scarabs, Zombies etc). If I were to make an example from the real world, it appears like an ancient Middle Eastern area. The area is essentially a large sand filled location with many underground areas (dungeon type). Expect to see many ancient artefacts and deserted ruins, as here is the location where the Mages imprisoned Durial.
: This area is very much like a rain forest and features many exotic yet not very surprising creatures (Pigmies!). It features a very expansive forest with deep swamps, as well as featuring a very prominent population of dangerous midgets with poisonous darts and have a cult like aura to them (their Shaman increase this feeling of a religious sect). Mephisto can be found in his underground lair, protected by his henchmen of death. These dungeon like areas are usually filled with endless hordes of creatures and can easily overwhelm under prepared groups.
: Welcome to hell. This area is nothing like what we know on earth, it is filled with the dead. If anything, the landscape is alien. As you seek deeper into the area, you will notice great lava rivers and molten rock. Diablo can be found in his sanctuary, a cathedral of sorts.
A mountainous region filled with hardy creatures, which have barred against the cold winds and the snow. It appears like a wasteland where a war has most likely been wage for some time. Baal resides in this area, although protected from the cold winter.