Global properties of an exact string theory solution in two and four   dimensions
  This paper discusses global properties of exact (in alpha prime) string theory solutions: A deformed black hole solution in two dimensions and a Taub-NUT type solution in four dimensions. These models are exact by virtue of having CFT descriptions in terms of heterotic coset models. The analysis includes analytic continuations of the metric, motion of test particles, and the T-duality which acts as a map between different regions of the extended solutions, rendering the physical spacetimes non-singular. 
Harald G. Svendsen