To

                                                        start

                                                 you

                                 need to

                         invent

                        gravity;

                           and give

                               it time to

                                   work its way

                                      with things.

                                   Then you find

                                a slope and add

                            some water, lots of

                      it, like from a dying

                glacier. Congratulations

         ! You’ve just made a river.