2D - How can I create an "inverted" circle collider?

I need to create a collider of the terrain in this picture:

alt text

I can not use polygon/edge colliders and I have no idea how to do the inverted colliders. :confused:

If what you want is a circle/sphere but that you can walk on the inside instead of the outside, then what you need is to make a sphere in a 3D program and invert its face normals and use that with a mesh collider component. Mesh collision is calculated on those, so if the sphere’s face normals are inverted, then it would be like having the earth hollowed out and walk on the inside. It would keep stuff from inside it, falling out.
Keep in mind though that what ever is outside the sphere will be able to get in. You’ll need a second sphere with its normals the right side out.
Also, don’t tick on convex as that means that the collider is filled.