  We develop a theory of static BPS domain walls in stringy landscape and
present a large family of BPS walls interpolating between different
supersymmetric vacua. Examples include KKLT models, STU models, type IIB
multiple flux vacua, and models with several Minkowski and AdS vacua. After the
uplifting, some of the vacua become dS, whereas some others remain AdS. The
near-BPS walls separating these vacua may be seen as bubble walls in the theory
of vacuum decay. As an outcome of our investigation of the BPS walls, we found
that the decay rate of dS vacua to a collapsing space with a negative vacuum
energy can be quite large. The parts of space that experience a decay to a
collapsing space, or to a Minkowski vacuum, never return back to dS space. The
channels of irreversible vacuum decay serve as sinks for the probability flow.
The existence of such sinks is a distinguishing feature of the landscape. We
show that it strongly affects the probability distributions in string
cosmology.
