I was invited for a second look and explicitly asked if there was someone/something in particular I wanted to meet/do.
I rounded with a general medicine team, attended morning report (I think), rounded with the GI consult team/attending, went on a tour of the GI endoscopy suite and saw some procedures being done, and then just walked around to some of the places where residents would be working (resident work room, clinic, etc). I was accompanied by one of the chief residents.
I attended noon conference and had lunch.
In the afternoon, I met the Chair of the Dept of Medicine, the program director, the GI fellowship program director, and some other faculty member.
They sure did cater to the fact that I was interested in GI and tried to assure me that I'd have no problem matching into GI if I attended their program. I ended up not ranking their program number one, but they sure did make that decision hard for me.
I would expect that you should have some questions and specific requests about how you would like your day to go. If not, then interview day was enough and why are you going?
Good luck!