A configuration of pseudo-Riemann geometry is considered representing a quasi-closed world in the form of a spatially closed universe connected with a mother universe along some world line. The classical and quantum theories of such a quasi-closed world are constructed in the minisuperspace approximation. The probability of tunneling of this world into a larger-scale region is calculated. Unlike the conventional approach to quantum gravity based on the time-independent wavefunction of the universe, our approach is free of difficulties related to the interpretation of the wavefunction since (1) the theory under consideration contains a time (the mother-universe cosmological time) in which quasiclosed universes evolve and (2) the quasi-closed universes form quantum ensembles with wavefunctions that admit the standard statistical interpretation.