Ravenholm is a small mining town and one of the locations visited by Dr. Gordon Freeman during the events of Half-Life 2. This town serves as an example to those who defy the rule of the Combine: the whole area is infested with zombies after the Combine bombarded the town with Headcrab Shells.
At some point following the Combine's conquest of Earth, Ravenholm became a haven for human citizens fleeing from City 17 and was used as a rallying point for the local anti-Combine resistance. However, the Combine discovered that Ravenholm was harbouring fugitives and punished the town by bombarding it with shells. These shells contained Headcrabs that attacked the townsfolk and turned them into host bodies. The zombies then attacked and killed most of the others, reducing Ravenholm to a ghost town.
Since the shelling, only one surviving resident of Ravenholm has remained: Father Grigori. Likely driven insane by his dire circumstances, Grigori has done well against the zombie hordes that roam the town. He has scavenged most of the town's remaining supplies to himself and set up multiple traps throughout the streets in an effort to destroy the zombie infestation. Such traps include flame-spewing devices, whirling propeller blades and cars turned into pulley-operated crushing weights.
During Half-Life 2, Gordon Freeman is forced to travel through Ravenholm after escaping Black Mesa East. There is little ammunition for him to pick up in the town, but fortunately he is armed with the Gravity Gun by this point, so he is able to use various objects strewn about the area - such as saw blades, explosive barrels and assorted debris - as his ammunition, using the Gravity Gun to fire these objects at sufficient velocity to slay any headcrabs or zombies that get in his way. With the aid of Father Grigori, Freeman survives Ravenholm and returns to City 17.