You are seeing the 3rd floor the enclosed roof HVAC units of the former Lucky Star Casino. Originally in that block of bldgs. you had the Golden Canary, The Lucky Star in the middle and Eureka at the end.
FYI: Fiztgeralds expansion is well underway, they have basically filled in the space between the Fitz's as you know it and the old Rohling Inn (another one of my old favorites!) Fitz's will now occupy that entire corner from the Gilpin to Crook's! They hope to be complete by June of this year. Eric