This level occupies the map slot MAP10. For other maps which occupy this slot, see Category:MAP10.
MAP10: The Black Gate is the tenth map of Requiem. It was designed by Orin Flaharty, with an ending provided by Adam Windsor (see Description.) The theme is quite similar the one throughout Ultimate Doom's fourth episode Thy Flesh Consumed. The map uses the music track "Lordly Might" by Mark Klem.
According to both the text file and the Requiem info pack:
Twisted demons created these repulsively evil buildings, as a battleground prepared against those who step within, and otherwise a place for defensive construction and research. It used to be a group of churches and embassies, where religious ceremonies took place thousands of years before the demons took over. Be well prepared for a showdown with a big demon as you get closer to the way out ...
Thanks to Adam Windsor for providing a revised ending of Orin's level after the original file corrupted.
After you teleport into the outdoor lava area, travel west across the ledge, and look at the southwest corner. Two patches of skin are present, and the westernmost one appears as a door on the automap. If it is shot, it will open. Hit it with the super shotgun, and do a running jump into the doorway; or do a running jump into this patch, and shoot it with any weapon. Proceed down the stairs to find a soul sphere. (sector 39)
At the southwest of the lava section are two small grates for lava to pass through. The texture of the northernmost one is not aligned properly. It can be walked through, allowing you to obtain a radiation suit and a megasphere. (sector 134)
Also in the lava section, to the southeast of the teleporter to the red key, there is another teleporter within the wall. Enter it to be taken to a platform east of the red key area. (sector 136) Look in the alcove to the east to find a box of rockets.