Each vault and crypt holds its own stories and secrets of the person entombed there. Have a look at Marathon Tomb if you enjoy contemplating lives and times past.
You're spoiled for sightseeing choice when visiting Marathon. Marathon Tomb is a great place to start here, but there are lots of other worthy attractions to check out. Schinias Beach, Marathon Beach, and Monastery of Saint Ephraim are near the tomb site and and will cap off your day nicely.