Aqueduct Opening
You can only do this on Fifth Jerusalem after you meet Allen at the hotel before heading up to your room go to cliff in the park and an old woman will be bothering a worker. Talk to her and then go back to the hotel and a man will be sitting in a chair wondering where his grandma is.
After you talk to him go back to the park and talk to the worker the her grandson will show up and take her away. The worker gives you a good item and walks away. You can now blow up the pipe and open the aqueaduct and get the item there.