  We study a class of non-geometric string vacua realized as completely soluble
superconformal field theory (SCFT). These models are defined as `interpolating
orbifolds' of $K3 \times S^1$ by the mirror transformation acting on the $K3$
fiber combined with the half-shift on the $S^1$-base. They are variants of the
T-folds, the interpolating orbifolds by T-duality transformations, and thus may
be called `mirrorfolds'. Starting with arbitrary (compact or non-compact)
Gepner models for the $K3$ fiber, we construct modular invariant partition
functions of general mirrorfold models. In the case of compact $K3$ fiber the
mirrorfolds only yield non-supersymmetric string vacua. They exhibit IR
instability due to winding tachyon condensation which is similar to the
Scherk-Schwarz type circle compactification. When the fiber SCFT is non-compact
(say, the ALE space in the simplest case), on the other hand, both
supersymmetric and non-supersymmetric vacua can be constructed. The non-compact
non-supersymmetric mirrorfolds can get stabilised at the level of string
perturbation theory. We also find that in the non-compact supersymmeric
mirrorfolds D-branes are {\em always} non-BPS. These D-branes can get
stabilized against both open- and closed-string marginal deformations.
