Just as it says "old dōjō". Its hard to provide any nuance or write down all the possible meanings without the surrounding context.
The meaning of "old" will depend on the context. Are you talking about the physical building? If so, then "old dōjō" will imply old, aged buildings. If you are talking about not only the building, but the activities of that building, it could have a more positive nuance: like venerable, unchanged, traditional.
But 古い道場 would rarely mean "our former dōjō" unless the context specifically made it clear that this is what you are referring to. But in this case, its still clearer to use 旧道場 (old/previous dōjō) or 以前に使っていた道場 (the dōjō that we used previously).