Traveler's Rest

The mysterious, spherical Traveler hovers above humanity's last city after saving them from destruction by alien forces.

The missing portions near the bottom of the sphere almost makes me think that humanity has in part built their city by removing pieces of metal from the Traveler.

As the huge, unknown artifact of Destiny, the Traveler would seem to be taking on the titular role in Halo.

Beneath-- and possibly reaching up towards-- the Traveler is the Tower, presumably a non-combat area where Guardian players will interact with each other.