Make something immovable to collision

How do I make a gameobject impervious to collision? Stuff bounces off it but it does not move. Temporarily I made it move massive, but that doesn't totally work after multiple collisions.

Thank you.

Instead of making the immovable object a rigid body and a collider, I just made it a collider and that worked.

Could you explain precisely how you did this? What settings are required? Setting isKinematic makes everything fly through each other anyway, nothing collides.