The Hall of the Dead is a synopsis of two pages that is well known as a Sprague de Camp and the comic versions in Marvel (Roy Thomas and Barry Windsor Smith) and Darkhorse (Busiek, Mignola, Truman and Nord, as could be seen in this post accompayining image)
But this series of posts is based on Howard's own stories so I'll go for the real synopsis.
Conan is in Zamora, pursued by soldiers. He has being a problem to the gobernor of a city. Conan manages to get rid of the soldiers. One of then, Nestor, keeps his pursue to find Conan trying to get inside the palace. After and argument, Nestor joins forces with Conan. There there are giant monsters and dangers that the two of them are able to pick some riches before an earthquake destroys everything.
After the robery, Conan and Nestor meet a girl in a tavern. They are drunk when the magistrate and some soldiers find them. Many jewels has turned to green dust. The magistrate opens a sack with a jade snake that transforms into a live snake. In the turmoil, the threesome escape.
More about The Hall of the Dead:
Image taken from Darkhorse.