You pry the sewer-gate open and enter

Kneeling down, you rest your hands around the wet, sewer gate. With a heave and a grunt, you manage to push it free and let loose a sound of screeching metal. Peering ahead, you see only darkness broken by patches of green bioluminescent moss on the walls. A rusty iron ladder can be seen near it, leading downwards.

You take a deep breath of cool air and move onwards. After all, you've already gone this far. Stepping into the sewer entrance, you make your way to the ladder and start climbing down. There's the wet, strange sounds of something below, slithering, and working away in their own time.