First of all, let me clarify some
things about the “infinite” maps:
They’re not infinite, but there’s no
hard limit either. It’ll just get
buggier and buggier the further out
you are. Terrain is generated, saved
and loaded, and (kind of) rendered in
chunks of 16*16*128 blocks. These
chunks have an offset value that is a
32 bit integer roughly in the range
negative two billion to positive two
billion. If you go outside that range
(about 25% of the distance from where
you are now to the sun), loading and
saving chunks will start overwriting
old chunks. At a 16/th of that
distance, things that use integers for
block positions, such as using items
and pathfinding, will start
overflowing and acting weird.
Those are the two “hard” limits.
Most other things, like the terrain
generation seeds and entity locations
use 64 bit doubles for locations, and
they do much subtler things. For
example, at extreme distances, the
player may move slower than near the
center of the world, due to rounding
errors (the position has a huge
mantissa, the movement delta has a
tiny, so it gets cut off faster). The
terrain generator can also start
generating weird structures, such as
huge blocks of solid material, but I
haven’t seen this lately nor examined
exactly what behavior causes it to
happen. One major problem at long
distances is that the physics starts
bugging out, so the player can
randomly fall into ground blocks or
get stuck while walking along a wall.
Many of these problems can be solved
by changing the math into a local
model centered around the player so
the numbers all have vaguely the same
magnitude. For rendering, Minecraft
already uses local coordinates within
the block and offset the block
position relative to the player to
give the impression of the player
moving. This is mostly due to OpengGL
using 32 bit floats for positions, but
also because the rounding errors are
extremely visible when displayed on a
screen.
We’re probably not going to fix these
bugs until it becomes common for
players to experience them while
playing legitimately. My gut feeling
is that nobody ever has so far, and
nobody will. Walking that far will
take a very long time. Besides, the
bugs add mystery and charisma to the
Far Lands.
In beta 1.8 the strange terrain may be gone, but some of the effects
aren't. After X/Z ±30,000,000 the world will start generating fake
chunks. Going into the fake chunks will result in falling into the
Void, and, subsequently, the player's death. If flying is used, going
about 34 blocks out of the limit will cause you to be stuck, being
able to use your inventory and look around, but not to move. Also, the
clouds will act strangely, moving at abnormally high speeds. Reloading
the save should fix the clouds, but the position glitch will still be
present. Also, at excessive X/Z positions, particles (rain, water,
snow, etc.) fail to appear staggered, instead forming rows of flat
"panes". The Far Lands do not lag in 1.8. in 1.0.0 the fire of torches
will be in/on a block next to it, instead of on the torch. In 1.0.0
explosion clouds look abnormally big. Piston heads will disappears
when the block is activated and will have the same effect as sand does
when falling (then disappears). Paintings can be placed over paintings
near the far lands. Also, the floating book in the enchantment table
seems to behave abnormally when a player is moving near it. Redstone
appears either extremely distorted, with stretched graphics, it can
appear misplaced, or it can appear completely invisible, but the
highlight box still appears indicating where redstone is placed.
Cauldrons, when looked from the inside, one of the sides is
translucent, and the graphics for that side appear one block away from
the cauldron on the opposite side of where the texture is missing
from. Highlight box for cake fails to appear correctly. Flames from a
monster spawner only appear on one side of the block. The graphic for
end portal block fail to appear correctly.
Best Answer
There is a deep pit with 4 chests (which contain various items: iron and gold ingots, diamonds, emeralds, bones...) and a pressure plate in the middle. Underneath the pressure plate are 9 blocks of TNT which explode after some time if you step on it.
The player in this screenshot is in the place of the removed blue wool block. One piece of sandstone at the bottom has been removed by me to show the TNT. The room is well lit because there is a hole in the ceiling right above the blue block.
You can easily avoid the pressure plate if you dig out one of the adjacent blocks to the blue one (note that now the pit will be much darker), but the fall is still quite deadly and takes 4 hearts.
And here is a video that demonstrates this: