OP is apparently looking for 1D structures:

1. On one hand, a 3+1D [Kerr black hole](https://en.wikipedia.org/wiki/Kerr_metric) has a 1D ring singularity.

2. On the other hand, an [event horizon](https://en.wikipedia.org/wiki/Event_horizon) has always [codimension](https://en.wikipedia.org/wiki/Codimension) 1 in spacetime. Subtracting 1 time-direction, we would speak of the event-horizon in 3+1D as an "area". In 2+1D that becomes a "length".