  It is still uncertain whether the cosmic censorship conjecture is true or
not. To get a new insight into this issue, we propose the concept of the border
of spacetime as a generalization of the spacetime singularity and discuss its
visibility. The visible border, corresponding to the naked singularity, is not
only relevant to mathematical completeness of general relativity but also a
window into new physics in strongly curved spacetimes, which is in principle
observable.
