  We have recently introduced a discrete model of Lorentzian quantum gravity,
given as a regularized non-perturbative state sum over simplicial Lorentzian
space-times, each possessing a unique Wick rotation to Euclidean signature. We
investigate here the phase structure of the Wick-rotated path integral in three
dimensions with the aid of computer simulations. After fine-tuning the
cosmological constant to its critical value, we find a whole range of the
gravitational coupling constant $k_0$ for which the functional integral is
dominated by non-degenerate three-dimensional space-times. We therefore have a
situation in which a well-defined ground state of extended geometry is
generated dynamically from a non-perturbative state sum of fluctuating
geometries. Remarkably, its macroscopic scaling properties resemble those of a
semi-classical spherical universe. Measurements so far indicate that $k_0$
defines an overall scale in this extended phase, without affecting the physics
of the continuum limit. These findings provide further evidence that discrete
{\it Lorentzian} gravity is a promising candidate for a non-trivial theory of
quantum gravity.
