In the warpgate area of Endless Gate, the player is able to venture outside of the intended playable area. It is possible to transverse the small platform behind it and see other areas of the map. Jumping off of the platform results in a death.
Apologies for weird crops, Steam didn't agree with me exporting screenshots, so I had to screenshot the previews and crop them myself.
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It ain't a new area Looks like that one Hive Queen related Strike Festering Core