untreaterd natural wood window cills

[TippyRabbit]

I have some light oak untreated window cills. The builders trod on them to get some height and have left dirty footsteps on them and cup marks.
I would be grateful for advice as to how I can remove these dirty marks before oiling them. I have tried bleach

You may have to sand them a bit with very fine sandpaper until you get the marks off.