From Bulbapedia, the community-driven Pokémon encyclopedia.
The Oreburgh Gate (Japanese: クロガネゲート Kurogane Gate) is a small cave that is located on the west side of Oreburgh City, separating it from Route 203. Although the passage between Route 203 and Oreburgh City is small, the cave has a lower floor that can be reached with Rock Smash. Underneath are several items and the only trainer in the game that uses Riolu, which can be reached using Strength and Surf. There are also ramps that can be jumped using a bicycle, formed naturally from the stone in the cave.