In the burn zombies burn pplace, you will see a tree in the back (just behind building) you can "climb" the tree if you walk at it from the right side, it may take a while to get, but it works!
Here is how you can walk on the benches in the Central Plaza.
The circular on around the tree is the easiest one.
Go to one end of the bench and sit. Get up and immediately try to walk down the bench. If done right, you should start to move up into the air and start walking on the bench.
The second glitch is located in the set of strait benches around the front of the mall.
go to the right end of the second bench and sit down. get up and try to walk to the gap between the first and second bench. You should end up walking on the first bench.
This one is a lot harder to do that the bench around the tree.