Does anybody know how to get on top of the Windmill Circle thing at Zanzibar?

I'm not sure what you mean about the windmill thing but I can help you get ontop of the Zanzabar Hotel.

When you first start the level (outskirts) go through the passage where you first see a grunt. Kill it and right before you go down the ramp look above you, there is a rectangle lamp.

Jump on top of it and move towards the slanted part above you, then jump up and crouch while in mid air and move forward if you do it right you will be above where the dead grunt is. (make sure to take srg. Johnson's Sniper Rifle (if you like to snipe because it's really good for sniping).

When you get to the top turn around and you can walk through the small alley and find the Cloak Skull (if you want it because it doesn't matter weather you have it or not. This is one of the most anoying part in the game (for me) look up slightly and you wil see a brown box sticking out of the wall.

Thats your ticket up, jump at an angle so you land on it(you know that you made it because your guy will not be on the ground). Walk forward above the alley and go as far as you want to the side and jump in the air, you should now be on top of the building.

Turn around and you will see another building infront of it, jump up and if done correctly you will be on top of that building. Now walk forward towards the little brown piece ahead of you and walk on it, when you get past it there will be a gap between one side of the building and the other. Jump across and walk forward untill you see a big bar thing that slants and goes strait and back down.

Jump on top and walk forward on it and turn to you left and there should be another building that you can jump on. Jump on it and walk to the right side and there will be another bar thing just like the one you used to get up on the building you are on right now.

Hop down and walk across the bar thing. Jump across the small gap or walk on the edge. Get down and walk on the edge of the building untill you see a fence on the edge of the building and when it shows "Checkpoint Done" you will see a pelican fly by and stop and stop near the ground.

That's you ride jump on top (it's best to jump by the nose of the pelican but make sure it's staying still). When on top walk to the right wing (opposite of the building you just jumped off) the pelican will start to fly jump on the building opposite of what side you were on. If you miss you can always restart from your last checkpoint.

When on top head torwards the jackals that snipe and jump across the building to the right of you and walk forward untill you see a big gray roof top next to the buildings you can get down or ignore it and keep waking further untill you see a slant.

Walk down it and and look for two air vent type things and jump on top of one then the other and jump up on to the roof next to them. Then you will see the Zanzabar Hotel. Walk of the roof and there should be a gap above the Hotel and drop down through the gap and there you go you just skiped half the level.

I do it all the time when I play the outskirts.

Have fun when you figure it out and also you marines kill all the Covenant aliens when your wondering around on the rooftops.

To get on top of the windmill on zanzibar you need to do this first get some s( plasma work best ) and you know that bridge thing up the steps that go to the windmill were you hit the glowing thing on the bottom to lower the bridge, don't lower it but instead find a way on top of the bridge when it is not lowered and throw a plasma under you when you are on top and jump ( crouch jump works best ) and go towards the top and you should get on top, once you do it and learn it well it gets pretty easy to do

Hope this helps :D