Spinning and twirling, Dante sailed his boat into the maelstrom. The crew did it so many times that everyone knew exactly how to handle things. When they came closer, they all let go of the control of the ship, letting it be taken into the void. The ghosts attached themselves to the railing on the sides to not be lost between the worlds.
To be ejected from the ship and end up to be a lost soul in the infinite darkness was the main danger of the crossing. The shadows between the worlds were nothing, it was no part of the Ombrae and no part of the light. Nobody knew what it was, they only knew it existed. Lights could be seen far away in the emptiness, showing the light worlds of the universe but that was all.