Copyright (c) 1995 Dave Thornburg

.This game is played on the following board.

CELL HEIGHT - The number of walls on that cell.
TURN - On each turn, each player must do one of the following things:
Move his stone to an adjacent cell, if that cell is not occupied by the enemy stone, and the number of walls it is not higher than the number of walls on the initial cell plus one.
The stone cannot be moved into the opponent's goal cell.
Place one or two walls on an empty cell.
Place one wall in a cell already with walls.
Walls may not be placed in a position that will eliminate all possible moves for an opponent to reach its goal cell. 
Walls can only be 5 stones high.
Wall cannot be build on goal cells.
GOAL - Wins the player that first reaches the opposite board cell (the goal cell).
However, each player has the right to have the same number of turns. So, if the other player also finish in the same turn, the game is a draw.

This game can also be played with 3 players, each one starting on an opposite hexagonal edge.

An example

The red stone is surrounded. Since it is on a cell with height one, he can move to any cell with height 0 (none), 1 (cell d8) or 2 (cells f9 and f10).

If the red stone was on a cell with no walls, and it was Black to move, he could not place a wall at d8, because the red stone could not move at all!

I wish to thank Peter Loop for rule clarifications.