Dungeon R2 starts from level 0
Dungeon R2 (shadowy dungeon) starts from level 0 (status bar displays level as "R2: 0") which seems unintentional as every other numbered dungeon starts at level 1.
Also death screen refers to this level as level 1 (dying on R2: 0 yields "She ended her adventuring life on level 1 of a shadowy dungeon.").