In string theory, black hole microstates at finite coupling give rise to horizon-scale structures that might solve the information paradox. Explicit constructions of these solutions are based on configurations of branes puffed up by the supertube effect. In an appropriate duality frame, we can construct the simplest supertube by adding momentum to a symmetric distribution of NS5 branes on their Coulomb branch. This suggests an exact worldsheet description of the supertube as a null gauged Wess-Zumino-Witten model. Such exact treatment in worldsheet string theory also describes BPS and non-BPS three-charge microstate geometries. This construction reveals stringy structures that are invisibile in the supergravity approximation, and that play a crucial role in understanding the constituents that carry most of the entropy.