I have access to a university's "Field House" as part of my gym membership. It is open for use a lot of the day, and is a large (i.e., BIG) room, hardwood floor, and with few obstructions (once you get away from the basketball hoops). It would seem to me to be a good place to practice casting . . . especially as the weather in Colorado turns colder.
My questions then are, "What would be the best ways of utilizing such a space?" Just general practice? Accuracy? Distance? Shorter or longer line length? Different "weights" of flies? Fake double-fly rigs (i.e., no hooks)? All of the above?