Shadows in my dungeon don't work

Hi, I'm new to BabylonJS and I need an advice concerning shadows. In the attached project I tried to make a little dungeon. There's a torch mounted on one wall with. The torch is the only source of the light in the cave. Walls behind the wall the torch is mounted on should be in the shadow but they are lit. I don't know why the shadow doesn't work. Please advise.

Thanks in advance. Vojtech.