In your situation I would stake out a trash can some place after Casey's Corner and before the hub. Find something you have with you that you can prop up the camera (maybe a shirt or a bag of some sort) a bit or so that you can angle it to view the Castle near the bottom of your frame with a lot of open space above the castle.
In this situation use a low ISO (ie 200), manual priority with a shutter speed anywhere between 2 and 5 seconds and set your aperture to f/5.6 or f/8. Don't release the shutter yourself. Use the self timer (at about a 5 second delay), this will help with camera shake from you pressing the shutter.
Another options is what others have also said, use ISO 400 or 800 (some camera's will lower the amount of megapixels at ISO 800, so be sure you know your camera). Use shutter priority and try slow exposures starting at 1/30th and lower (1/15th, 1/8th). Sitting on the ground with your knees up, holding the camera with 2 hands braced against your knees, or lean against a fence or pole, again try using the self timer and hold your breath (litterally, even breathing could give camera shake).
FYI: Keep in mind that you can buy table top tripods, that are small enough to fit in your pocket, at just about any camera store (ie: Ritz Camera) for less than $20.
