Eren let his blood drop right in the middle of the depression over the stone platform. Immediately afterwards, a strange mana pulse was released in the surroundings with the altar as the epicentre of it.
The skull with the two horns levitated in the air while the altar split vertically right in the middle. A thin, semi-transparent mana layer was created in the space that was open by the split altar. That mana layer looked like the surface of a lake, with ripples forming in between.
Next, the horned skull turned around on its own and radiated a blinding red light that fell on the water-surface-like mana layer. As a result of which, the ripples stopped forming on the surface and became stable.
This was a subspace that led to the Oni dungeon. A subspace was different from a separate dimension. It was still part of the same dimension. It was just that it was isolated from the rest of the world in various ways.
