The Union Square, Somerville, watering hole Backbar literally fits its name. It’s tucked behind its hip sister restaurant Journeyman, down an adjacent hallway and through a large steel door. Journeyman itself is off the beaten path, a hard right onto Sanborn Court — more of an alleyway — from the square’s central parking lot. Once you find Backbar, you’ll discover a dimly lit cocktail lounge, serving a rotating menu of specially crafted drinks that have quickly garnered a reputation as some of the area’s best. As it prepares to celebrate its one-year anniversary next month, owner Tse Wei Lim, who also runs Journeyman with his wife, Diana Kudajarova, talked about Backbar’s becoming a crowded hot spot.