Moonriver Inn is best accessed by car. It's an approximately 2 to 2.5 hour drive from Manhattan depending on traffic.
From the upper deck of the George Washington Bridge, take the first exit to Palisades Parkway North. Stay on the Palisades Parkway for about 18 miles, and take exit 9W to 1-87 North (to Albany). After approximately 24 miles on 1-87, you'll see signs for US-6/NY-17 W/Harriman - stay in the right two lanes, and merge onto NY-17. Note there is a toll here. Stay on NY-17 W for about 46 miles, and take exit 104 to NY 17-B Monticello/Raceway. Stay on 17-B for 24 miles to Route 52 W (it's a left turn about 7 minutes after you pass Bethel Woods on the rightside). Take Route 52 W to where it intersects with Route 97 and turn right. This road turns into Bridge Street. After you enter Narrowsburg, pass the first stoplight, pass the library, the Tusten Theater, and Moonriver Inn is two doors down on the right. The driveway is a right turn off of Bridge Street after you pass the Inn, and parking is in the back.