Sokoban

Sokoban is a game invented by a Japanese company, "Thinking Rabbit". Essentially, it's the Block Puzzle of all Block Puzzles.

The idea is simple: Push all of the blocks inside a maze on their target positions, but there are two rules that make it tricky:
 * You cannot pull blocks; you can only push them.
 * You cannot push more than one block.

Suddenly a task that seems so simple becomes really challenging. In other words, the game can get very hard, very fast.

A lot of people liked the idea and now there are tons of remakes and new levels on the Internet. Many of them are rather difficult.

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 * Back Tracking: Since you can only push one block at a time, you will have to traverse the map multiple times. This is amplified in some layouts (e.g. Level 20), where you need to traverse the entire level to get a box around a corner.
 * Block Puzzle: The ultimate.
 * Follow the Leader: Aside from thousands of straight remakes, the basic mechanics have themselves became a standard for most puzzle games with blocks.
 * Lost Forever: You cannot retrieve a block pushed in a corner, or next to an edge wall. If one of the target squares is right there, it's all fine, but if not, then...
 * Unwinnable By Mistake: Very rarely, some poorer clones/remakes feature levels that are unsolvable from the very start.