What awesome images are suggested by the existence of such secret cities within cities! Beholding this ingulph’d and search-defying fragment of yesterday, the active imagination conjures up endless weird possibilities - ancient and unremember’d towns still living in decay, swallow’d up by the stern business blocks that weary the superficial eye, and sometimes sending forth at twilight strains of ghostly music for whose source the modern city-dwellers seek in vain. Having seen this thing, one cannot look at an ordinary crowded street without wondering what surviving marvels may lurk unsuspected behind the prim and monotonous blocks.

— H. P. Lovecraft, The letters of H.P. Lovecraft (via)