Stone Barns is a actually a part of the Rockefeller State Park Preserve. Hiking Trails will take you along the picturesque Swan Lake and you can wonder through to the back of Stone Barns to check out their "wild life" including sheep, turkeys and pigs. The trails are easy for walking with clearly marked signs and dog-friendly. I definitely recommend walking the grounds at some point during your stay.
Quaint house of famed American writer, Washington Irving, who wrote The Legend of Sleepy Hollow and Rip Van Winkle. This is directly across from Lyndhurst Castle and only 5 min away from the wedding site. You can easily visit both Sunnyside and Lyndhurst in the same day.
Home to the Rockefellers, this Castle boasts beautiful views of the Hudson as well as an equally beautifully decorated interior where one can get a glimpse into the lives of the Rich & Famous of Old New York. Just a stones throw from Sunnyside, be sure to visit both!
This is a favorite art spot of mine and Virgil where you can rent bikes or hike around the 500 acres of outdoor sculptures and enjoy the glorious fall foliage. There is a little cafe for a light seasonal bite or a hot drink to warm you up. As Fall is the busiest time of the year, I recommend visiting on a weekday or arriving early on a weekend.
Also within close proximity to the Wedding site, Dia Beacon is an indoor art museum boasting a wide collection of both paintings, sculptures and installations from the 60s to present day.
Most highly regarded cooking school with 4 restaurants to choose from ranging in style from Italian to French to American Nouveau. It is a good excuse to go further up the Hudson and I would suggest staying around Poughkeepsie for an extended stay if you wish to add on to your trip. Check out The Mohonk Mountain House as a place to stay.