  We discuss the structure of a gravitational euclidean instanton obtained
through coupling of gravity to electromagnetism. Its topology at fixed $t$ is
$S^1\times S^2$. This euclidean solution can be interpreted as a tunnelling to
a hyperbolic space (baby universe) at $t=0$ or alternatively as a static
wormhole that joins the two asymptotically flat spaces of a
Reissner--Nordstr\"om type solution with $M=0$.
