Piranesi's Imaginary Prisons are one of my favourite series of prints. Up there with 36 View of Mount Fuji by Hokusai, albeit in a different medium since they are etchings instead of woodcuts.
The story behind them is that many artists during the 18th century were forced to make prints for rich tourists from other European countries who were doing the Grand Tour. Often the features of major landmarks like the size of the coloseum were exaggerated to make the prints more impressive. The Imaginary Prisons series of prints takes all of this embellishment and inverts it to create a series of fantastical, claustrophobic dungeons. They are very gothic and have impossible architecture which may have inspired later artists like MC Escher. I also personally think they might have inspired the architecture in the Dark Souls video game series.