The Prison City of Hell's Reach is a d20 System scenario for characters of any level. Part of AEG's Adventure Keep line of short, cheap modules in half-sized format (4-1/4"x11"), it is intended to be run as a single session. From the back cover:

According to myth, Hell spewed forth a foul seed of its damned terrain that took root in the world and yielded the ruined city known as Hell's Reach. Once a prosperous trading port that harbored pirates, outlaws, and worse within its walls, the gods themselves punished the city for turning its back on its one-time patron deity and embracing decadence, greed, and violence. A tremendous earthquake sundered the peninsula that connected the city to the mainland, leaving it a half-flooded island populated by small bands of desperate survivors. Hell's Reach is now a dumping ground for criminals deemed too dangerous to ever allow back into society and too likely to break free from prison.

Though warships constantly patrol the waters around Hell's Reach, travel to and from the city is not impossible. Smugglers and other criminals use magical means to ferry weapons, armor, and other goods to the ruins, trading such mundane items for poisons and worse. As a one-time prosperous port, many fabulous treasures lie hidden within the city's crumbling walls, and more than a few daring bands have ventured into the city. Those that make it out speak of desperate bands of cannibals, highly organized criminal gangs, and much worse that stalk the streets. Yet these same survivors often return laden with gold, jewels, and magic.