During Harry Mason's search in Silent Hill, he must eventually descend into the sewers underneath Silent Hill. He does so twice: once in order to reach the Resort Area (by descending down a manhole near Midwich Elementary School, as advised by Lisa Garland) and again through the manhole on the west end of Sandford St. (by the docks). The first time around, Cybil Bennett secretly follows Harry; the second time, he follows her into Lakeside Amusement Park.
The sewers beneath Silent Hill are an extensive collection of large passageways, and many of the walls and ceilings are adorned by what Dahlia Gillespie claims to be the "Mark of Samael". Most of the tunnels have curved ceilings, however some open up to large rooms where water and sewage are held. There are no lights within the sewers so Harry must rely on his flashlight and the map to guide him through the various intersections. Though the water appears shallow and small boats can sometimes be seen floating on the water, only dry concrete and metal flooring is traversed while underground. Hanged Scratchers and Stalkers are encountered for the first time in the sewers, while Creepers and Mumblers can also be encountered. Blood appears on many surfaces, though the cause for this is unspecified. In-game, the sewers are split into three explorable sections:
Connecting to Resort Area
Harry first enters the Sewers through the town's Waterworks facility next to Midwich Elementary School. He does so to reach the Resort Area on the southern end of town. The sewers connecting to the Resort Area are split into two levels. The ladder Harry uses to enter leads to the lower level. The area is mainly composed of two large horizontal passages and one vertical passage. There is a large room-sized area on the northeast, where a desk and supplies can be found. In order to exit this level Harry must obtain the Sewer Key, which unlocks the gate (marked blue) on the southern passageway. The ladder at the very bottom of the map leads to the next section of the sewers, the upper level.
The upper level of the sewers (relative to the map) is composed of two large horizontal and two large vertical passageways arranged in a sort of rectangle. The lower longitudinal passageway is marked by various gates, one of which is locked. Like the section before it, this level of the sewer requires a key, the Sewer Exit Key, in order for Harry to finally exit the sewer system and enter the Resort Area using the ladder at the southeast corner of the map. This part of the sewer venture becomes the most dangerous, and grabbing the key from the bloody water triggers an immense number of Hanged Scratchers and Mumblers to chase after him, and while he runs, the ground in some areas will collapse to slightly alter his path.
Connecting to Amusement Park
Harry enters the Silent Hill sewer system in order to catch up to Cybil Bennett, who had left for Lakeside Amusement Park before Harry. A brief cutscene shows Cybil being attacked by an unknown foe (setting up the latter boss fight). Cybil, and eventually Harry, enter this section of the sewers through the manhole on the west end of Sandford St. This section, unlike the previous two, is under the effects of the Otherworld shift experienced earlier, and many floors and walls are adorned by what Dahlia Gillespie claims to be the "Mark of Samael". Much of the ground and walls have become rusted metal grating, shrouded corpses can be seen hanging about and large holes have appeared, blocking progress. No key is required to unlock any gates, and after reaching the west passageway Harry will come upon an area containing objects from the park above, and a ladder to exit the sewers once and for all.
Silent Hill: Shattered Memories
After the car ride with Michelle Valdez and John nearing the end of the game, Harry Mason must go through the sewers to reach Lakeside Amusement Park. The sewer area is much shorter and straightforward than it is in in the original game and there are no locked doors nor monsters of any kind.
There is a U-shaped area in the tunnels where Harry can find the "A Happy Bond" memento, obtained by trying to remove a hook from the mouth of a fish in a pipe. Harry can also find and take a photo of an UFO behind the gates near the exit ladder.