In front of Parliament, the traditionally costumed evzones (presidential guards) stand by the tomb and change every hour on the hour. On Sunday at 11am, a whole platoon marches down Vasilissis Sofias to the tomb, accompanied by a band. The evzones uniform of the fustanella (white skirt) and pom-pom shoes is based on the attire worn by the klephts, the mountain fighters of the War of Independence.
You can also see evzones outside the Presidential Guard and nearby Presidential Palace. It's interesting to see them here, alone and away from tourist cameras, going through their ritual pomp even in the dead of night.