Harbat-folk are by nature old-fashioned and greedy: they tend to keep close what they have - a trait developed by the fact their city is situated on an island, not much room for innovative and expansionistic thinking. The dead are revered by all. On the other hand, the dead are utterly useless. No need to waste too much space on them. But we must honor grandfather (he was a lieutenant on a seaship), so he'll need a big and ornate tomb! What to do?
Expand inward. The whole of Harbat's underground is littered with tombs: dark hallways cut in the very rock filled with tombs, and a great cavern with mist clinging the graves there. The entrance is a dreary stairway in Barrow's End. It is said that the cemetery has access to several underground caverns and caves. What lies there, no one knows.