Sentinel Prime

Sentinel Prime is the capital city of the Night Sentinels (or Argentians), located on the planet Argent D'Nur. This was once the sprawling capital of the Interstellar Sentinel Empire, but by the events of Doom Eternal the city is a husk of its former self and under occupation by the Hell Priest Deag Grav who hosts brutal gladitorial battles with demons there. This is alike the rest of Argent D'Nur, which has been conquered by the forces of Hell and the maykr. Unlike most other sentinel cities visited by the Doom Slayer, Sentinel Prime is actually inhabited to some extent, as the Doom Slayer meets several Night Sentinels at the heart of the city. The population most likely lives in oppression and constant fear under their overlords, and appear to revere the Doom Slayer as a leader of the city rather than Deag Grav - as the former was supposedly a sovereign there at some point. It is in Sentinel Prime that the Doom Slayer fights the great demonic champion of the arena - The Gladiator, and kills the Hell Priest Deag Grav. According to sentinel customs, if the Doom Slayer spills sentinel blood in the capital, he loses his authority there and may be apprehended. Since Deag Grav used to be an Argentian, this would create an issue in killing him, but it is possible the Sentinels would eventually forgive this given the circumstances.

Description
Sentinel Prime appears to have a cascadian landscape alike most other Sentinel cities, and appears to be within a subarctic temperate region, dominated by vast mountains and conifer forests. A single moon is visible in the sky, with a reddish surface colour not unlike Mars. At the heart of the city lies the gladitorial arena, where the champions of yore would fight mighty battles, and where condemned criminals were offered a chance for pardon though trial by combat. It was here that the Doom Slayer once proved himself worthy of living amongst the Sentinels long before the city fell under Deag Grav's control.