The Dungeon Corridor is a long, gloomy stone passageway that leads from the narrow spiral staircase coming down from the Viaduct Entrance to the staircase leading down to the blank stone wall which is the entrance to the Slytherin Dungeon. The Potions Classroom can be found along this corridor. The Slytherin Corridors are probably adjacent to this corridor.
She'd gotten a bit lost looking for their Common Room, but thought she was headed in the right direction now. She'd spot Tessa coming her way and move to one side of the corridor to keep out of her way.