Add Holes to Object

I'm trying to make a 3D version of a Labyrinth game, and I need to make a playing field with holes in it that the player can fall through. I made a model in blender with "holes" in it, but my gameobject in unity treats the whole blender object as a solid plane and glides right over them. Is there a way of having unity recognise the holes in the model as non-solid? I'd prefer not to use blender at all, but the very few things I could find about using 3D objects for this kind of thing suggested it's not possible to put holes in them with unity. Is there a way to add holes in the editor, or if not, how can I remove collision from the holes in the model? TIA