  Cosmological constant a.k.a. dark energy problem is considered to be one
major challenge in modern cosmology. Here we present a model where large scale
structure formation causes spatially-flat FRW universe to fragment into
numerous `FRW islands' surrounded by vacuum. We show that this mechanism can
explain the origin of dark energy as well as the late time cosmic acceleration.
This explanation of dark energy does not require any exotic matter source nor
an extremely fine-tuned cosmological constant. This explanation is given within
classical general relativity and relies on the fact that our universe has been
undergoing structure formation since its recent past.
