  The existence of genuinely non-geometric backgrounds, i.e. ones without
geometric dual, is an important question in string theory. In this paper we
examine this question from a sigma model perspective. First we construct a
particular class of Courant algebroids as protobialgebroids with all types of
geometric and non-geometric fluxes. For such structures we apply the
mathematical result that any Courant algebroid gives rise to a 3D topological
sigma model of the AKSZ type and we discuss the corresponding 2D field
theories. It is found that these models are always geometric, even when both
2-form and 2-vector fields are neither vanishing nor inverse of one another.
Taking a further step, we suggest an extended class of 3D sigma models, whose
world volume is embedded in phase space, which allow for genuinely
non-geometric backgrounds. Adopting the doubled formalism such models can be
related to double field theory, albeit from a world sheet perspective.
