The Void
The Void is an entity in space. It appears as a location in Wonderland east of the Forever Forest in Wonderland Secret Worlds, but is independent from Wonderland in Wonderland Adventures. It is a dark place where all the colour of Wonderland has been taken away. In Wonderland Adventures, it is also the home of the Thwarts.
Wonderland Secret Worlds
In Wonderland Secret Worlds, the stinkers had to get across The Void to rescue the Wee Stinkers that were blown away by a violent storm.
Wonderland Adventures
In Wonderland Adventures, the Rainbow Shards that gave Wonderland all it's colour were taken by the Thwarts. This caused the Void's energy to creep into the rest of Wonderland. The Thwarts took the Purple Shard into the Void. It had to be rescued and taken back into Wonderland to save Wonderland's colour.
In the latter part of the trilogy, The Void is home to the Retro World and the disjointed Flash practice room.
Trivia
In Wonderland Secret Worlds, one must only need to complete the secret level "Escape from The Void" and ignore all other levels in The Void in order to make progress towards beating the game.