Would you be interested in growing mushrooms? There is a variety of them out there, and you'll have to make a choice first before making the necessary modifications of the barn, like limiting the light coming in.
If your barn is sturdy enough, it could be used for storage. My parents used their old barn to store tractors, extra feed, and so forth. Do you have a newer barn where you keep livestock? What would you do with the space if you tare down the old barn?
You'd be surprised how long well built barns will stay standing. We've got a 140 year old barn, many others around here still standing. Some get fixed up and that's nice too if you've got the time to devote to it. For that project I'd like to mill my own barn boards from the property. Nothing more proud than building from the land you stand on.
Depending on the condition ... there are many options.
In addition to the ones listed above, if it really is beyond salvage by either repair or selling the lumber - you might see if the local fire department would like to burn it for you as a training exercise.