-▶ swipl -s treasure_hunt.pl
    Welcome to SWI-Prolog (threaded, 64 bits, version 9.2.9)
    SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
    Please run ?- license. for legal details.

    For online help and background, visit https://www.swi-prolog.org
    For built-in help, use ?- help(Topic). or ?- apropos(Word).

    ?- start.  % <- this

    Enter commands using standard Prolog syntax.
    Available commands are:
    start.                  -- to start the game.
    up. down. right. left.  -- to go in that direction.
    ...etc...