There is a moon and a city inside your lung. Inside of your lung there is a city and above that city lies a moon. It’s a pretty sight, but also very strange. Moons and cities don’t usually reside inside lungs.
Having a moon and city inside your lung inspires you to write a haiku (はい). Perhaps the city and moon are just metaphorical. Either way, a haiku is the best way to go about things here.