They invite you to this interview day with a bunch of other potential interns. They then feed everyone breakfast and welcome them with a bunch of speakers. Next 3 employers of different departments that they select as best fit according to your resume come and interview you separately. You discuss your resume with them and then you go sit down to have lunch and fill out some papers regarding what department you want to work in and which you want to avoid completely. The three employers will then discuss your resume together to see which department you best fit into. Finally you go home and wait to hear back an offer from a department.