Sacred Haven of Debauchery

The monsters are defeated without any resistance.

Is it difficult?

I don't remember at the beginning, but later on, tougher monsters will appear and start dominating. Although, I'm not sure what determines the strength of a monster; maybe it's based on their level, or maybe it depends on how far you've progressed in the game.
Yesterday, my brother was running around in some cave, and there was a mountain inside. He was climbing it, and a bear fell from the top and killed him.