Outskirts vacation
From Halopedia, the Halo wiki
The Rooftops Vacation, or simply, the rooftops, is a small programming oversight, similiar to The Delta Halo Vacation, The Metropolitan Vacation, and The Cairo Station Vacation. it allows you to reach areas of a level previously thought to be inaccessible.
How to reach it
Enter the courtyard and kill all the enemies until the hunters come out. Kill them as well. Then go through the tunnel-type thing the hunters made, but do not continue through. Instead jump on top of the protruding wall. Then crouch jump onto the wooden support beam overhead. You should see three pipes coming out of the wall and into the ground, of progressingly larger heights. Jump onto the bottom one an crouch jump onto the remaining two, and then the actual roof. Now you can roam around this part of the level, and find a bunch of neat things to explore. It is suspected that you can reach the next part of the level this way, with the sputnik skull, but it hasn't been tried yet.
