A thorough treatment of Raumschach can be found on the Chess Variant Pages (http://www.chessvariants.com/3d.dir/3d5.html).
The starting position is as shown here, and pieces move similarly to chess. There is one new piece, the Unicorn, which moves more diagonally than the Bishop.

Included as a variant is what I call Alice Raumschach. As in Alice Chess, pieces flip between two parallel universes when they move.

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