Sewers are, in most cases, designed to be invisible. Deep underground, they ferry urine and feces (and other things) out of sight, and few people give them much thought until something goes wrong, when murky water fills the basement or some stench drifts up from below. 

But the history of sewers, in all their smelly glory, deserves a closer look. These essential networks revolutionized urban living, sparked reams of lore, and inspired grand civic monuments. From odes to the workers keeping cities unclogged to excavated slabs of filth to an ornate tunnel with marvelous acoustics (and a supremely fancy lighting scheme), here are 13 places to learn about these underground worlds.