  Microswimmers are exposed in nature to crowded environments and their
transport properties depend in a subtle way on the interaction with obstacles.
Here, we investigate a model for a single ideal circle swimmer exploring a
two-dimensional disordered array of impenetrable obstacles. The microswimmer
moves on circular orbits in the freely accessible space and follows the surface
of an obstacle for a certain time upon collision. Depending on the obstacle
density and the radius of the circular orbits, the microswimmer displays either
long-range transport or is localized in a finite region. We show that there are
transitions from two localized states to a diffusive state each driven by an
underlying static percolation transition. We determine the non-equilibrium
state diagram and calculate the mean-square displacements and diffusivities by
computer simulations. Close to the transition lines transport becomes
subdiffusive which is rationalized as a dynamic critical phenomenon.
