  We construct stationary Ricci-flat inter-universe Lorentzian wormhole
solutions in all D\ge 5 dimensions that connect two flat asymptotic spacetimes.
Such a solution can be viewed as the gravity dual of a string tachyon state
whose linear momentum is larger than its tension. We focus our analysis on the
D=5 wormholes which are not traversable for the timelike and null geodesics;
however, we demonstrate that there exist accelerated timelike trajectories that
traverse from one asymptotic region to the other. We further study the
minimally-coupled scalar wave equation and demonstrate that the quantum
tunnelling between two worlds must occur. We also obtain charged wormholes in
five-dimensional supergravities. With appropriate choice of parameters, these
wormholes connect AdS$_3\times S^2$ in one asymptotic region to flat
Minkowskian spacetime in the other.
