This is my Halo 3 Sky Fort, map (Avalanche) and gametype.

The attackers must use the vehicles located in the garage at the bottom of the map to deliver the bomb to the sky fort, located at the top of the map. There is a ramp so the vehicles can drive up.

However, the defenders must hold their ground at the top of the sky fort, fending off all the attackers with their limited supply of weapons.
Whole Map: http://s647.photobucket.com/albums/uu191/PopcornColonel/?action=view&current=20090426-144507.jpg
Sky Fort Spartan Side 1: http://s647.photobucket.com/albums/uu191/PopcornColonel/?action=view&current=20090426-144449.jpg
Sky Fort Spartan Side 2: http://s647.photobucket.com/albums/uu191/PopcornColonel/?action=view&current=20090426-144445.jpg
Sky Fort Covenant Side: http://s647.photobucket.com/albums/uu191/PopcornColonel/?action=view&current=20090426-144418.jpg
Garage and Air Base: http://s647.photobucket.com/albums/uu191/PopcornColonel/?action=view&current=20090426-144323.jpg
Ramp: http://s647.photobucket.com/albums/uu191/PopcornColonel/?action=view&current=20090426-144349.jpg

Located here: Bungie.net : Halo 3 File Details

or in my file share: Bungie.net : Halo 3 File Share

Gameplay: *NOTE*: this was on a WAY earlier version of the map, so the map is close, but not really the same. The ramp has been fixed and the the map has been balanced.

http://www.youtube.com/watch?v=u-JO87150Hk&fmt=22