Seed : CouplerBattleRailgun (Beta 11.1)
There's a long two-tile wide corridor leading into a wall (behind which is another corridor) and nothing else in -2/Testing, located below the Alpha 7 testing range at the top-left of the map. I thought i took a screenshot, but apparently i forgot to. (Second time i forgot to take a screenshot to report a prefab(?) bug in testing.)