  An exact and analytical solution of four dimensional vacuum General
Relativity representing a system of two static black holes at equilibrium is
presented. The metric is completely regular outside the event horizons, both
from curvature and conical singularities. The balance between the two
Schwarzschild sources is granted by an external gravitational field, without
the need of extra matter fields besides gravity, nor strings or struts. The
geometry of the solution is analysed. The Smarr law, the first and the second
law of black hole thermodynamics are discussed.
