Looking for both casual or fancy for a 5 day trip.
I LOVE Naples. We have a condo there and I try to go twice a year. I am a fisherman so I definitely recommend that. I usually go to Key West or the Everglades. There are many guides to choose from. If you want to learn about the mangroves and local wildlife there are kayak tours you can take. Naples Bay has a harbor cruise. We did that once. You see the houses of CEOs and dolphins will usually follow along side you. 3rd St S and 5th Ave S areas are great places for restaurants and shopping. You really can't go wrong with just about any of them. I personally like Bistro 821and Bleu Provence. For breakfast check out Goldies Restaurant and/or Bill's Cafe on 3rd Ave N. You HAVE to check out the beaches and there are plenty to pick from. The further away from the Naples Pieryou are the better shot of getting decent parking and a less crowded spot on the beach. The water will be cold but you'll get some sun without the heat.
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Do you like French food? If so, Escargot 41 is a great little hole in the wall that's really pretty reasonable. Needless to say, their escargot is amazing!