Abstract: We will discuss some Hardy inequalities and its consequences on the large time behavior of diffusion processes. Roughly speaking, the Hardy inequality ensures a further and faster decay rate. Two differente situations will be addressed. First we shall consider the heat equation with a singular square potential located both in the interior of the domain and on the boundary, following a joint work with J. L. Vazquez and a more recent one with C. Cazacu. We shall also present the main results of a recent work in collaboration with D. Krejcirik. In which we consider the case of twisted domains. In this case the proof of the extra decay rate requires of important analytical developments based on the theory of self-similar scales. As we shall see, asymptotically, the twisting ends up breaking the tube and adds a further Dirichlet condition, wich eventually produces the increase of the decay rate.