Complex sentence: The five-story building where Marks & Co. was located during the novel's action still exists, and has a small round gold-coloured plaque mentioning the memoir on a pillar of the outer wall.
Split into simpler sentences: The five-story building still exists where Marks & Co. was located during the novel's action. It has a small, round, gold-coloured plaque mentioning the memoir on a pillar of the outer wall.