Take the ferry to Martha's Vineyard and Nantucket! The ferry to Martha's Vineyard leaves right from Falmouth (Woods Hole) and then you can island hop to Nantucket. Martha's Vineyard can definitely be done in a day trip, whereas Nantucket is a bit further and is most likely an overnight. Martha's Vineyard is a bit bigger and more casual, whereas Nantucket is more upscale. Both are very bike friendly, so renting bikes is a great way to see the islands. In Martha's Vineyard, check out Edgartown (the Harbor Lighthouse is beautiful) and Oak Bluffs for shopping/restaurants, the infamous Jaw's Bridge (you can jump off if the tide is right), and lots of beaches. Nantucket is known for their shopping and it is hard to find a bad restaurant or beach. Cisco Brewers original location is also on the island and a ton of fun.
Chatham is another beautiful spot, located at the "elbow" of the Cape. Chic boutiques reside in quaint storefronts along its winding Main Street lined with historic inns, white-steepled churches, trendy eateries and art galleries. Stage Harbor Light, located near Harding’s Beach, and scenic Chatham Light, which overlooks Lighthouse Beach and currently serves as an active U.S. Coast Guard station. The Chatham Bars Inn is one of the most beautiful resorts on Cape Cod, so it is worth a stop for lunch or drinks.
The Beachcomber in Welfleet is a must-visit if you are staying, it does close in early October, so take a look at the hours before planning. This restaurant/bar sits on top a dune overlooking Cahoon Hollow Beach (along the National Seashore). There is a raw bar, great food and cocktails, and often live music. You can make a day of it and go to and from the beach and restaurant. Parking can be limited and costs money (but is used as a voucher at the restaurant). They do provide a shuttle from larger lots if it is full.
Provincetown aka "P-Town" is located at the very tip of the Cape. It is a lively, walkable town that is known for its beaches, harbor, artists and LGBTQ community. Race Point beach is beautiful and you can check out the Pilgrim Monument in the center of town. If you venture to the top, you are able to see all of Cape Cod.