In Sewer Crawler, you play as a sewer scavenger, a wage worker in a futuristic cyberpunk dystopia. Your job is to explore the dark underground labyrinths of the city's sewer system, searching for treasures and the totem hidden within each level while managing your flashlight battery and oxygen and escaping hostile creatures. You must find the totem before you can leave the sewer and return to the city's surface.

The surface functions as a hub where you can talk to eccentric characters, enjoy their humorous dialogue, spend your coins at the shop on valuable items such as medkits, batteries, and oxygen, and prepare for your next expedition.

You can tackle the sewer levels in any order you choose. The game features five sewers, each with a distinct environment and its own combination of four different horror enemy archetypes, ranging from creatures that stalk and pursue you to enemies that only move when you're not looking, and others that can teleport around the environment and damage you when you look at them. Each enemy's unique behavior can generate unpredictable, emergent jumpscares.

Completing a sewer creates an autosave checkpoint, so if you die, you can continue from your most recently completed sewer level.