I had multiple phone interviews with the HR manager as well as multiple media planners before coming in for an office interview. At the office interview, I was there for almost three hours and sat in one room where about 5 different people came in to talk to me. The office is pretty open but doesnt have many perks of an agency atmosphere such as a bar, lounge chairs, drinks, food, etc. The dress is very casual - jeans and flip flops.