Age

An Age is a Minecraft dimension generated by Mystcraft.

All ages will have Abandoned Libraries. Various features, such as caves, ravines, villages, etc., may be found, and potentially at higher frequency than in the vanilla overworld. Or, they might not be found at all.

Most ages will not have vanilla-like biome layouts. Ages may have biomes that cannot normally be found in the vanilla overworld (this requires having biome-adding mods that do not put their biomes in the overworld). Rivers, Oceans, and "border" biomes—shores, edges, beaches, etc.—will be the biggest changes from normal. Instead of being special-cased edges, they will be the normal biome size—so a river in a Mystcraft age will behave more like a lake, or a mushroom island shore will behave like a shallow ocean with no hostile mobs underground. The exact nature of the biomes depends on the Biome Controller—for example, Tiled Biomes are single-chunk alternations that, because of their small size, have a lot of landscape features of their neighbor biomes.

Lands may be "normal", or they may be flat, caveworld (nether-like), void, etc.

Skylands can be (very rarely) found in any type of world, and will generally carve the world into large numbers of small islands.

Transportation
To travel to a new Age, players may Link by using a Descriptive Book either from a held book or a stand. The player will be transported to the Age with their inventory and experience, but the book will not travel with them. If the book was on a stand then it will remain there. If the book was in the player's inventory, it will fall to the ground, open Books on the ground will take damage from rain and water, and anything that can hurt an entity such as a player. Books on the ground also take damage over time, so a book stand is the safest way to store a book.

Ages are generated based on the Symbols contained within the Descriptive Book used to link. When using a blank Descriptive Book, symbols will be automatically selected. If a player wants to customize their own age however, they can use a Writing Desk to copy symbols to and from their personal Notebook.

Players must be wary when traveling between ages: in order to get back to where they were before traveling to an age, the player will need a Linking Book created in the exact place they would like to return to. If a player forgets their Linking Book, they will usually be trapped with no way back to where they started. Their only hope is to find a Star Fissure to get back to the Overworld spawn.

Spawn platform
Generally you will want to surround the initial spawn platform in a building to act as a safe shelter from monsters, as well as to house the return linking book in order to protect it from rain, water, and explosions. It should be noted that the ceiling will need to be 4 blocks off the ground (or more) where the player spawns, or they will spawn on top of the roof the next time they use a linking book to enter the age.

Instability
Ages may also be unstable, leading to Decay or, as of 0.9.3.0, various potion-like effects that are triggered by sky exposure, or air exposure, or just being in the age. Most of the spreading decay blocks, like Goo, will replace most or all of the blocks in the world. Black decay is the "ground destroying" decay that collapses the ground and ultimately exposing the world to the void.

Additional forms of instability include meteors, constant lighting strikes, faster block ticks, or erosion—which replaces dirt with sand, and stone with gravel, logs with planks, etc—or other effects.