Inter-linked levels

For cases where this is unusual, excluding most (even all?) console games. MMOs should not be tagged with this, nor adventure games, nor console-style RPGs.

This is half-way solution between the old linear level progression with no backtracking of any kind to previous levels and seamless worlds. A retardation in game engine technology that persists for some unknown reason, though it does make things like MMOs easier to manage (distribute user loads between servers) in some aspects.