Ladder

Ladders are wooden blocks used for climbing walls either vertically or horizontally. They can only be placed on the sides of other blocks.

Occurrence
Ladders occur naturally in Strongholds in library rooms and intersection rooms with a wooden ceiling. Ladders can also be found in NPC Villages, specifically, in tall buildings and houses with roofs which have fence railings.

Placement
Like torches, a ladder occupies one block from the side on which it is placed and cannot be placed on glass, leaves, Ice, or Glowstone Blocks. Unlike torches, however, they resist water and will create an air pocket. They also resist lava, and can be used instead of glass to let lava light shine through a ceiling. If you place a ladder in lava or water just on the ground not near a wall, the air pocket will be present but invisible.

Usage
Ladders provide a way to safely cushion a player's impact after a free fall. Upon entering a ladder's area of effect, the player's speed is reduced instantly to normal ladder descent speed and no damage is taken.

Holding the sneak key while climbing a ladder will grab hold of the ladder, to prevent you from falling off. When the player is holding on to a ladder, the rate which blocks are mined decreases.

Any mob can climb a ladder in the same way a player does: by pushing against it. Mobs are not smart enough to deliberately use ladders — they won't stay on a ladder to get somewhere — but a ladder directly in their straight-line path will let them climb up.

How ladders work
A ladder takes effect whenever your lower half is in the cube occupied by a ladder. These effects are:
 * If you push against a wall, you move upward instead. (Thus inside a 1×1 ladder shaft, you can use any movement key to move upward.)
 * If you are moving perpendicular to the ladder block and you enter the ladder block, you will begin to move upwards, but you will most likely fall off the ladder shortly, seeing as you will continue to move horizontally.
 * Your maximum downward speed is reduced to a “descending ladder” speed.
 * Your horizontal movement friction is the same as on ice. (That is, moving around in the tiny space you can be in while still hanging on the ladder at the same level.)

History
Ladders were added in Infdev (June 7, 2010).

Pressing the sneak key to stop moving down the ladder was added in Beta 1.4.

Before Beta 1.5 ladders could be placed on every other block and still be climbable, because you could climb a ladder when any part of your body was on it, not just the lowest part. As well, the ladder crafting recipe produced only one ladder per 7 sticks instead of two; thus the 1.5 changes did not change the number of sticks needed to make a ladder of a given height.

On the Beta 1.6 update, it was made impossible to place ladders on Glowstone

In the 1.1 update, ladders did not have collision boxes, but were readded in 1.2

In the 1.2 update, the crafting recipe produces three ladders per 7 sticks, as apposed to 2 in 1.1

Trivia

 * It takes approximately 110 seconds to travel from bedrock to the roof of the sky on ladders as seen here.
 * If you place a bucket of water in a place occupied by a ladder with no other blocks next to it, the water will replace the ladder and you will not get the ladder back.
 * It is possible to use ladders one block apart in a corner by placing every other ladder on the other side of the corner. This method is a bit hard to use, as you will need to jump and shift sides constantly, but it works!
 * By holding the jump key, players can still use water ladders that have ladders placed every other block.
 * If you stop yourself on a ladder and place a sign, you will still stay in midair without having to hold Shift since the game is paused in singleplayer. This does not work in multiplayer since the game is not paused.
 * Attempting to place a ladder on a spot another ladder occupies may instead place the ladder somewhere near by.
 * It is possible to remove a ladder while standing on a ladder and holding the sneak key, but it can take a long time because the countdown for breaking the ladder often resets.
 * If you place a block while on a ladder then try to remove it, it is slow, as if you're underwater, presumably because you're holding onto the ladder with one arm.
 * Unlike walking, consuming food does not slow you down while climbing ladders.
 * The ladder texture is invisible from the back, as seen in some strongholds where ladders spawn without a block behind them. Unlike vines ladders will remain climbable from the visible side and can not be walked through from the invissible side.
 * Like vines, ladders slow you down when walked through.