Probably just a good cleaning to remove dirt and oils that have helped
darken it will make a difference, Im sure there are professional locals
that know how to clean it and not ruin the wood. Sanding once started
must be complete and uniform, with the woods age you have no idea how
deep oxidation goes, but it is probably oxidised throughout so real
lightening might be impossible. You need pro local advise, consider
lighting and a good decorator to get the most out of what you have. And
forget the sandblast idea.