This trick requires an AT-4 or an RPG-7. Go to the roof of the 'hotel'-like location. Stand on the part of it when you need to actually jump high on. When standing on it, take out the AT-4 or RPG-7. Go to crawl mode then back up. When you see your character start to lean back, hold Analog-pad Up until you put you hands up on the thing, as if you were going to climb it, but with the AT or RPG. After you do this correctly, walk over to the big, green, slanted like object. Do not take off the sentinel. Start walking or running toward on the bottom part of it. Sooner or later, you will get up on it. Walk up the whole thing and walk off of it. However, you will not actually get off of it. You will start walking like normal. Also, if you listen carefully you will hear the sounds as if you were walking on it normally, and not flying.