I would like to know if there are compact (n-1)-manifolds $N$ that are not spheres but such that there is a manifold with boundary $M$ which satisfies the following two properties: - $\partial M\cong N$ - $M-\partial M\cong \mathbb{R}^n$ I am primarily interested in this question in the category of smooth manifolds but I would be interested to know the answer in the topological case as well.