Sentence:  The famous champion, St. Andrew of Scotland, travelled through ayale of walking spirits, most fearful to behold, and had not seen the light of the sun or moon for seven days, but was guided by a <WSD>walking fire</WSD>, till he came to a castle, before which lay the giant whom St. Anthony slew, his flesh was rent and torn by wild foxes, crows, and such like. 
Meaning of the word marked with <WSD> tags:  Will o' the wisp