We LOVE Misquamicut State Beach in Westerly, Rhode Island. It's about a 20-30 minute drive from the hotel. There is a fee to park, so ride together :)
We recommend the Andrea or the Windjammer for food/drinks if you go!
We also love Narragansett Town Beach, although a little farther (about 45 minutes). You can usually find street parking if you leave early enough and pay to go onto the beach.
We recommend the Coast Guard House for dinner/drinks or Monahan's Clam Shack for snacks!
Catch the sunset from Watch Hill, walk past Taylor Swift's house, window shop the boutiques and grab some ice cream! Fun fact, Watch Hill is where we had our engagement photos taken :)
From the Mystic Marriott, you are only:
an hour from Newport, Rhode Island
an hour and a half from Boston
2 hours from Cape Cod
3 hours from Portland, Maine