It is prominent as being one of the more odd levels, and for containing the "Death Replicator" an obscure boss enemy that was cut from the final release of Ecco 2.
The representation of the Vortex airships and structures as imagined through this level paint a much darker portrait than that of the finalized version. A blood red sky glows against the backdrop, and various sinister machines, some of which do not appear in Ecco 2, are inherent in this early build onthe Dark Vortex Future. The Ecco 2 level Black Clouds echoes a lot of the eerieness garnered from this stage.
Numerous traps and obstacles fill this level, ranging from sporadic electrical currents to motion-activated metal needles that try to impale Ecco. Devices which spew toxic bubbles also exist within this bleak stage.
(note that other stages use the "H" ambiguously as titles at times, although this is the most prominent)
While the level is not large by any means, it does contain a boss. A cyborg dolphin appears in the southwest corner of the level, and will actively attack Ecco while a scrolling crab on the ceiling drops bombs from above.