that is a monstrous freaking barn.
If you epoxy and want it darker, I would buy some transtint dye and mix that in with the epoxy, you can adjust the concentration and work towards a rough color tone of what you want. Though for use inside, epoxy will be expensive and probably overkill, but done right, it would fill the cracks and give you a smooth surface. I would consider maybe just spraying it down with some shellac for a buildup coat, then wipe on/spray on a topcoat. With all of those cracks through, a brushon will be prone to having the finish build up and run. A spray on finish would give you a better chance of an even, smooth finish. If you wanted to really level things out, look for a high solids spray on finish, this will level more quickly and give you a thicker coat(though not fill the cracks). That is unless you want a raw look and feel to the wood, then a light wipe/brush on would work.
[This message has been edited by agrams (edited 8/13/2013 2:34p).]