Anthill. a is where you fall in. Each symbol represents a vertical
tunnel you have to go up 3 or 4 times from a to reach the surface.

--------------------------------------------------------

                a
                |
                1

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                1
                |
            4-3-2

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              3           6    :
             / \         /
            4---5     2-1

--------------------------------------------------------

            4                  :
                              /
                             6
                            /
                         2-1
                        /   \
                @-9    5     8

--------------------------------------------------------

              ?-@       8
                       /
                    #-9

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               ?