  Fix a strictly positive measure $W$ on the $d$-dimensional torus
  $\bb T^d$. For an integer $N\ge 1$, denote by $W^N_x$, $x=(x_1,
  ..., x_d)$, $0\le x_i <N$, the $W$-measure of the cube $[x/N,
  (x+\mb 1)/N)$, where $\mb 1$ is the vector with all components equal to 1. In
dimension 1, we prove that the hydrodynamic behavior of a superposition of
independent random walks, in which a particle jumps from $x/N$ to one of its
neighbors at rate $(N W^N_x)^{-1}$, is described in the diffusive scaling by
the linear differential equation $\partial_t \rho = (d/dW)(d/dx) \rho$. In
dimension $d>1$, if $W$ is a finite discrete measure, $W=\sum_{i\ge 1} w_i
\delta_{x_i}$, we prove that the random walk which jumps from $x/N$ uniformly
to one of its neighbors at rate $(W^N_x)^{-1}$ has a metastable behavior, as
defined in \cite{bl1}, described by the $K$-process introduced in \cite{fm1}.
