The Plaza Premium lounge in the domestic terminal of Penang airport is accessible via Priority Pass, and it’s located just past where you clear security.
It’s a relatively small lounge, but there’s a fair amount of seating, and it wasn’t crowded at all when I was there.
For a domestic lounge, I thought there was a surprisingly decent food selection. There was fish ball noodle soup, curry, mixed vegetables, pasta with Alfredo sauce, barley soup, and congee. Definitely enough to have a filling snack before a flight.
The wifi worked okay, and the lamps scattered throughout the lounge had USB chargers, but I couldn’t seem to find any normal outlets, which I found confusing. But overall, I found this to be a very pleasant domestic lounge with pretty good food options and comfortable seating.