I like to practice karate on the beach. Besides being a totally different terrain to practice on, beach training allows me to get into the moment of the kata. If I close my eyes and listen to the surf crash and smell the salt air, I can almost create a picture in my mind of old Okinawa, practicing alongside one of the karate masters of old.
If you do practice on the beach, I would recommend a time that you won't attract too much attention to yourself. Early in the morning, around sunrise, the majority of people on the beach seem to be runners, a few fisherman and surfers. This is a good time to practice as most of them won't stop and gawk or ask quetions and interupt your training. They are too busy with their own activities to care what you are doing.
In general, I don't like to practice in public, because I don't like spectators. If people do stop and watch, I will generally stop doing karate and just stretch or walk.