Sand neck is hands down my favorite beach on the cape. I can sum up why with two words, "sand bars". This is at low tide, high tide is never as fun, but that goes for every ocean beach. There is no other beach in my opinion on the cape that has better swimming conditions. You can walk a good hundred feet out and still be able to stand on the sand below. The waves are not big, but they are always fun to ride into shore by just floating. The one downside is that the water is always a bit colder, but that has never been a big deterrent.
If you are not swimming you can walk for miles and miles. While walking I have always found the best sea creatures at sandy neck, from big crabs to my favorite starfish. Near the shore there are areas of small rock that hide all sorts of creatures, which is one of the main reasons that I am so enamored with starfish. The sand is also really good for building, and it never fails that I end up helping my younger cousins build a huge dam to hold back the water flowing out from the sand bars with the tide.
The fun does not stop at night, you are allowed to drive out and build a bon fire on the further parts of the beach. Summer would not be complete with out smores on the beach.
If you spend some time on the cape during the summer you must check out sandy neck, you do not know what you are missing!