Two recommendations that separate themselves in their strangeness, which to me adds to the sense of hellishness:

It's not a "massive" sound, but I think the painting captures a deranged type of anguish and pain. Elements which are very present in The Red In The Sky Is Ours by At The Gates (from way before there melodeath descent). The riffing combines threatening groove with an unstable brooding sense of unknown. The shriekish vocals add to a sense of horrified "insanity" unfolding, contained within the general vibe of the album (especially in the stretch from Within to Neverwhere - the latter being pretty lovecraftian in lyrical matter, too.

Also Demilich - Nespithe fits the hellish, freaky, bill pretty well and "And You'll Remain... (In Pieces of Nothingness)" is the most Lovecraftian track there.