What's the nearest place to Rhinebeck where I can go boating or kayaking?

The Kayak Festival in Kingston is really fun, and a great way to spend some time on the water, and while I don't know if you can go kayaking in Legion Park, you can always head over to the Hudson River, where they have plenty of relaxing yet strenuous kayaking adventures!

There is actually a Kayak Festival I just found out about in nearby Kingston, NY (about 3 miles away). It is on the Hudson River, yes, and it starts at Kingston Point Beach. They offer classes and activities for everyone from first time paddlers to more experienced ones. They also have demos of new equipment and such. There are also Kayaking Programs which include tours of the Hudson such as the Good Morning Paddle and the Hudson Sunset River Paddle. You can find out more info by checking out the Forsyth Nature Center website.