Caelid is the one area in that most players dread, either through the memes, or the fact that it's visually horrifying with its red sky and dead ground.

Source: https://gamerant.com/elden-ring-pushed-through-wall-fall-death/

The Battlemage Hugues is inside the Sellia Evergaol, southwest of Fort Faroth in Caelid.

Source: https://gamerant.com/elden-ring-caelid-bosses-locations-drops/

The Flame Prophet starts at the Smouldering Church, on the border of Caelid and Limgrave's northeast.

Source: https://gamerant.com/elden-ring-convergence-mod-all-new-classes-modded-class-starting-locations-equipment-overview/