This is one of Robert E Howard’s contributions to the Cthulhu Mythos, and a personal favorite of mine. It was published posthumously in 1936.
A Lovercraftian tone started to settle over the story as the heroes entered a lost desert city, but then switched to an exciting brawl described in bone-crunching detail as the heroes confronted human foes in the form of Clarney’s old enemy Nureddin el Mekru and his band of Bedouins. The finale switched back to Weird Tales horror with yet another “indescribable” horror out of the Cthulhu playbook, but at the end, instead of mythos dread, I was left with a sense of exhausting exhilaration, the thrill of seeing tough characters skirt the edge of danger and madness and emerge—changed, but still holding onto the vitality of survival, which is ultimately all that seems to matter to them.
The full text of this story can be read here.