  We consider the focusing energy subcritical nonlinear wave equation
$\partial_{tt} u - \Delta u= |u|^{p-1} u$ in ${\mathbb R}^N$, $N\ge 1$. Given
any compact set $ E \subset {\mathbb R}^N $, we construct finite energy
solutions which blow up at $t=0$ exactly on $ E$.
  The construction is based on an appropriate ansatz. The initial ansatz is
simply $U_0(t,x) = \kappa (t + A(x) )^{ -\frac {2} {p-1} }$, where $A\ge 0$
vanishes exactly on $ E$, which is a solution of the ODE $h'' = h^p$. We refine
this first ansatz inductively using only ODE techniques and taking advantage of
the fact that (for suitably chosen $A$), space derivatives are negligible with
respect to time derivatives. We complete the proof by an energy argument and a
compactness method.
